I discovered today that FaceTime didn’t work on my iPhone 4: people couldn’t start FaceTime calls with me and I didn’t have any of the FaceTime buttons present. Turns out that this problem is caused when restoring from an iPhone 3G running iOS 4 — it seems the FaceTime on/off setting is imported from the iPhone 3G (which has it turned off as it doesn’t support FaceTime). Going into Settings > Phone and then flipping FaceTime on solved it for me.

Other people seem to have had to jump through a couple of extra hoops to get this to work, if flipping the switch didn’t get you going, take a look at this post over at the Rusty Brick blog.

Update 2010-08-22: Still having trouble? Did you jailbreak your iPhone 4? There’s something else that might stop this working too.

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That was a bit odd. My iPhone 3G started acting a bit weird so I turned it off. I turned it back on, and it took what seemed like forever to start back up.

When it eventually did come back, it was deactivated! It had the connect-to-itunes image (not text like the image above) at the top of the screen, no service name in the top-left corner, a “slide for emergency” thing at the bottom and an info button which showed the ICC ID and IMEI.

In a bit of a panic I turned it off and on again.

It took another eternity to start back up.

And then it booted normally, with the “iPhone is activated” message. Is my iPhone dying, or is it just time for a factory restore in iTunes?