Your phone quietly chooses between three different technologies every time you send a message. You never see the decision, but it changes what the message costs, how it is delivered, whether your recipients end up in a shared thread, and whether the picture you attached arrives looking like it did on your screen.
Most of the confusion around green bubbles, group texts that split apart, and messages that cost three times what you expected comes down to not knowing which of the three was used.
The three at a glance
| SMS | MMS | RCS | |
|---|---|---|---|
| Stands for | Short Message Service | Multimedia Messaging Service | Rich Communication Services |
| Introduced | 1992 | 2002 | 2008, revived from 2016 |
| Carries | Text only | Text, images, video, group threads | Text, media, typing indicators, read receipts, reactions |
| Length limit | 160 characters per part | Effectively unlimited text | Unlimited |
| Media size | None | 300 KB – 3.5 MB, carrier dependent | 100 MB typical |
| Travels over | Carrier signalling network | Carrier data | Internet |
| Needs a data connection | No | Yes | Yes |
| Works without a plan | No | No | No |
| Group threads | No — separate messages | Yes | Yes |
| Typical cost | Per message on your plan | Often billed above SMS | Free, consumes data |
| Delivery reliability | Very high | Good | Depends on both ends |
| Delivery receipts | Optional, carrier level | Optional | Yes, plus read receipts |
| Encryption in transit | No | No | Yes |
SMS: the one that always works
SMS is the oldest and the most dependable. It rides on the signalling channel the network already uses to manage your phone’s connection to the tower, which is why it works with no internet connection, on any phone made in the last thirty years, and in places where data has given up entirely.
Its limitation is in the name: it is short, and it carries text only. It also has no concept of a group. Sending to ten people means ten separate messages that happen to contain the same words. Each recipient sees a normal one-to-one conversation with you, and none of them can see the others.
MMS: the group mechanism, by accident
MMS was added to carry pictures. Along the way it became the mechanism for group threads, and that second job turned out to be far more consequential than the first.
When your phone puts several recipients in one conversation where everyone sees everyone, it is sending an MMS. This is why an ordinary text “becomes an MMS” the moment you add a second recipient to the thread — and on many plans, MMS is billed differently from SMS, or counted against a separate allowance.
MMS does not really travel as a message. Your phone uploads the content to your carrier’s server and sends a small notification; the recipient’s phone downloads it over data. That is why an MMS can sit at “Downloading…” on a bad connection, and why carriers impose a size cap that silently recompresses your photo into something blurry.
RCS: the modern replacement
RCS is what SMS would look like if it were designed today: effectively a messaging app running over the internet, but built into the phone’s default messaging rather than requiring an install. It gives you read receipts, typing indicators, reactions, high-quality media and proper group threads.
Google pushed it for years on Android through Google Messages. Apple added support in iOS 18, which is why iPhone-to-Android messaging improved noticeably from late 2024 onward. Before that, every message between the two platforms fell back to SMS or MMS — the origin of a decade of green bubble complaints.
The catch is in the last column of the table: depends on both ends. RCS works when the sender, the recipient, both carriers and both messaging apps all support it. When any link is missing, the message silently falls back to SMS or MMS, and you are not told.
How your phone decides
Nobody chooses a protocol from a menu. The phone decides, in roughly this order:
- Are both ends on iMessage? On iPhone, if the recipient is a registered iMessage user and you have a data connection, the message goes as iMessage — Apple’s own service, not any of the three. Blue bubble.
- Is RCS available on both ends? If not iMessage, and both sides support RCS with a working data connection, it goes as RCS.
- Is there more than one recipient, or an attachment? If RCS is unavailable and the message needs a group thread or carries media, it goes as MMS.
- Otherwise, SMS. Plain text, one recipient, or everything above failed.
The important consequence: you cannot force a protocol. There is no setting that says “send this as RCS”. You can disable things — turn off iMessage, turn off RCS, turn off MMS Messaging — but you can only ever push the phone down the list, never up.
What changes with more than one recipient
This is where the three diverge sharply, and where most surprises live.
| Behaviour | SMS (individual) | Group MMS | RCS group |
|---|---|---|---|
| Recipients see each other | No | Yes | Yes |
| Replies go to | You only | Everyone | Everyone |
| Recipient limit | None practical | 10–25, carrier set | 100 typical |
| One person can derail it | No | Yes | Yes |
| Someone can leave | N/A | Not reliably | Yes |
| Personalisation possible | Yes | No | No |
| Cost per extra recipient | One more SMS | Usually flat | Free |
Two things are worth pulling out.
Group MMS has a hard recipient ceiling set by your carrier, commonly between 10 and 25. Exceed it and behaviour varies from silently dropping the extra recipients to splitting the thread into several groups to failing outright. The per-carrier numbers are in carrier limits for mass texting.
Group MMS cannot be personalised. One message goes to everyone, so it cannot contain a name. If you want “Hi Marco” and “Hi Anna”, you need individual messages — which is the entire subject of group text versus individual texts, and the reason the choice matters more than it first appears.
Mixed recipient lists
Any real list of customers, parents or club members contains both iPhone and Android users. Here is what actually happens.
From an iPhone. iMessage users get iMessage. Everyone else gets RCS if their side supports it, otherwise SMS or MMS. In a group thread, one non-iMessage participant is enough to drop the entire conversation to group MMS for everybody — which is why adding one Android friend to a family thread changes the colour and loses the features for all of them.
From an Android phone. iPhone recipients get RCS on iOS 18 or later, and SMS/MMS before that. Android-to-Android is RCS where both have it enabled.
What this costs you. Your plan’s SMS and MMS allowance is consumed only by the part of the list that fell back. You cannot predict which part, and it changes as recipients upgrade their phones. For a list of any size, budget as if all of it is SMS.
Character limits, encoding, and why a message costs triple
This is the single most expensive detail in mass texting, and it is invisible until you look at a bill.
SMS encodes text in GSM-7, a 7-bit alphabet covering plain Latin letters, digits and a small set of symbols. That gives you 160 characters in one message.
The moment your text contains a single character outside that alphabet, the whole message switches to UCS-2, a 16-bit encoding, and the limit drops to 70 characters.
| Message content | Encoding | Characters per part |
|---|---|---|
| Plain Latin text | GSM-7 | 160 |
| Plain Latin, split across parts | GSM-7 | 153 |
| Any emoji, curly quote, or many accents | UCS-2 | 70 |
| UCS-2, split across parts | UCS-2 | 67 |
Two consequences that catch people out:
Concatenation costs you characters. A long message is split into parts and reassembled on arrival, but each part spends 7 characters on the header that says how to reassemble it. So 320 characters is not two messages of 160 — it is three parts of 153.
One emoji rewrites the whole message. Not just its own part. A 150-character text with one 👍 at the end is no longer one message: at 70 characters per part it becomes three. To 200 recipients, that is 600 messages instead of 200.
If you write in Italian, French, Spanish or German, this is not an edge case. A single è, ü or curly apostrophe from autocorrect is enough. The practical advice is to write in plain ASCII for large sends, and to check the character counter your messaging app shows before pressing send.
When RCS falls back, and how to tell
RCS silently degrades, which is a good design for reliability and a bad one for predictability. It falls back when:
- the recipient’s phone or carrier does not support RCS
- either side has RCS turned off in messaging settings
- there is no data connection on either end
- the recipient is roaming on a network without RCS interconnect
- the group contains at least one participant who cannot receive RCS
You can usually tell after the fact: RCS threads show typing indicators and read receipts, and in Google Messages the input field says “RCS message” rather than “Text message”. On iPhone, an RCS thread is green — the same colour as SMS — but the field reads “RCS Message”. Confusingly, green no longer means “this is SMS”; it means “this is not iMessage”.
Is RCS encrypted?
Partly, and the honest answer has changed recently enough to be worth stating carefully.
RCS is encrypted in transit between your device and the messaging server, which SMS and MMS are not. Google Messages has added end-to-end encryption for RCS conversations, one-to-one and group, when both sides use Google Messages.
Cross-platform end-to-end encryption — iPhone to Android — was not part of the RCS Universal Profile that Apple shipped in iOS 18. The GSMA published a Universal Profile revision adding end-to-end encryption based on the MLS standard, and platform support has been rolling out since. If this matters for what you are sending, verify the current state on your own devices rather than trusting a general claim: the answer depends on both participants’ apps and versions.
What is not in question: SMS and MMS have no end-to-end encryption at all, and carriers retain metadata for both. For anything genuinely sensitive, a dedicated encrypted messenger remains the right tool.
Does it still make sense to use SMS at all?
Given that WhatsApp, Telegram and RCS all exist, it is a fair question. SMS keeps two advantages that matter specifically for announcements.
It arrives. No app required, no account, no internet connection, no friend request, no algorithm deciding whether to show it. If the number works, the message lands. Open rates for SMS remain far above email precisely because there is no inbox competing for attention.
It reaches everyone. Your list contains people who do not use WhatsApp, people on older phones, and customers who gave you a phone number and nothing else. SMS is the only channel that covers all of them without asking anyone to install anything.
The cost is real, which is why the encoding section above deserves a minute before you send to a few hundred people. And the consent dimension is real too: a channel that always arrives is a channel people resent being used badly. Anyone sending at scale should be able to say where each number came from and how someone stops receiving messages — the subject of consent and opt-out.
Questions people ask
What is the difference between SMS, MMS and RCS?
SMS carries plain text over the carrier’s signalling network with no data connection required, limited to 160 characters and with no group support. MMS carries media and is the mechanism behind group threads, travelling over carrier data. RCS is the modern internet-based replacement with read receipts, typing indicators and large media, which falls back to SMS or MMS when either end does not support it.
Why did my group text become an MMS?
Because a shared thread where everyone sees everyone is delivered as group MMS. SMS has no concept of a group, so the moment you put several recipients in one conversation the phone switches mechanism.
Is RCS better than SMS and MMS?
For features and cost, yes: unlimited length, high-quality media, read receipts, and it uses data rather than your message allowance. For reliability, no — SMS works with no internet connection and on every phone, which is why RCS falls back to it rather than replacing it.
Does RCS work between iPhone and Android?
Yes, since iOS 18, when both devices, carriers and messaging apps support it. Before iOS 18, iPhone-to-Android always fell back to SMS or MMS, which is where the green bubble reputation came from.
Why do some of my messages count as two or three?
Because they exceed the per-part character limit: 160 for plain Latin text, 70 if any character falls outside the GSM alphabet. Split messages also lose 7 characters per part to reassembly headers, so the real limits are 153 and 67.
Should I avoid emoji in a mass text?
If cost matters, yes. A single emoji switches the entire message to 16-bit encoding and drops the limit from 160 characters to 70, which can turn one message per recipient into three.
Is MMS more expensive than SMS?
On many plans, yes — MMS is frequently billed separately or at a higher rate, and it consumes data on both ends. Check your plan before sending pictures to a large list.
Why is my message green if RCS is supposed to be modern?
On iPhone, green means “not iMessage” — it does not distinguish RCS from SMS. Check the text in the input field: it reads “RCS Message” on an RCS thread and “Text Message” on an SMS one.
How many people can be in a group MMS?
Carrier dependent, commonly between 10 and 25. RCS groups typically allow around 100. Exceeding the limit produces inconsistent behaviour — dropped recipients, split threads, or outright failure.
Can I choose which protocol my phone uses?
Not directly. The phone picks the best available option automatically. You can disable iMessage, RCS or MMS in settings to push it down to a simpler protocol, but there is no way to force a message up to one the recipient cannot receive.