Contact recently upgraded to iPhone. How can I tell my iPhone to send them iMessages now?

One of my contacts has recently switched to an iPhone. How can I tell my phone to send them iMessages now?

Solution 1:

It ought to figure it out for itself, once their phone is set up correctly.

So long as their phone number is listed in their phone, in Settings > Messages > Send & Receive as "You can be reached by iMessages at..." then it should just switch over.

You'll see their messages start to appear in blue rather than green.

You can test/check by finding them in Contacts. As you open their details, you should see FaceTime light up, which confirms they're on an iPhone.