What is the difference between iMessage and SMS?

The short answer

iMessage is Apple's own service. It works when everyone in the thread is on an iPhone, iPad or Mac with a data connection. When one person is on Android, or the data connection drops, Messages sends a text message instead and the bubble turns green. You are not switching apps. Messages does both jobs in the same window, and the colour is the only thing telling you which one just ran.

What changes with the colour

• Who carries it. Blue goes through Apple's servers over Wi-Fi or mobile data. Green goes through your mobile carrier, the same network that carries your calls.
• Encryption. iMessage is encrypted end to end, so only the devices in the conversation can read it. SMS is not; it crosses the carrier's network as plain text.
• Photos and video. Blue sends them at close to full quality. A green photo goes as MMS, which most carriers shrink hard. That grainy picture from a friend with an Android phone probably looked fine when it left their hand.
• Length. A single SMS holds 160 characters. A longer green text is split into pieces and put back together on the receiving phone.
• The extras. Read receipts, typing dots and editing a sent message are iMessage features. Plain SMS has none of them.

Green does not always mean SMS any more

RCS is the carrier industry's replacement for SMS, and iPhone has supported it since iOS 18. It brings typing indicators, read receipts and better photo quality to conversations with Android. The bubbles stay green. So a green bubble is now one of two things: old-style SMS or MMS, or an RCS message that looks the same. Whether you get RCS depends on both carriers, which is why a green thread can start behaving differently without you changing a setting.

Where the colour starts to matter

On a Windows PC, the colour disappears. Phone Link connects to an iPhone over Bluetooth and relays one-to-one texts, blue or green, as they arrive, but it cannot tell the two apart. It shows no history in either colour, no group chats and no photos, for reasons built into the connection.

The phone itself does not keep them apart. It stores every message in one database and records on each one which service delivered it; the blue and green you see is that record, painted. Read the database instead of the screen and both colours come back together, in order, with the exact time on each.

Keeping both colours in one place

ScribeHold does this on Windows, reading the same database the phone keeps, so blue and green arrive on your PC together with their attachments and the name of whoever sent each message in a group. It needs a USB cable and your passcode, typed on the phone. Each bubble keeps its colour, so a mixed thread reads as the one conversation it was. RCS messages show green, the same as SMS; ScribeHold does not mark them separately.

It reads; it never writes to the phone. It also cannot send a reply.

When this page is as far as you need to go

• If you only wanted to know what the colours mean, you now do. Nothing above needs software.
• If you want to text from your PC, this is the wrong tool. Phone Link does that job for one-to-one chats, and it is free.
• It cannot bring back what the phone has erased. Once iOS has purged a message, ScribeHold will not find it, in either colour. If a legal matter turns on it, ask a forensic examiner, not us.
• Windows only. ScribeHold does not run on a Mac.

If you do want the whole thread, check it is still on the phone first: scroll back to the oldest message you can reach. If it is there, download ScribeHold for Windows. The free tier searches everything you have; opening conversations past 90 days and exporting past 30 is ScribeHold Complete. If the reason you want the thread is a dispute, start with whether screenshots are enough for court.