According to Apple’s official iOS 5 features page, messages sent or received through iMessage should automatically sync between your devices. Unfortunately, that doesn’t always work right out of the box. Fortunately there is a simple way to make it work.
From Apple:
Start here, finish there
Begin a conversation on one iOS device and pick it up on another.
The issue is with which address is set as your Caller ID. By default, the iPhone is set to use your phone number as the caller ID, whereas the iPod touch and iPad are set to use your email address.
Setting your caller ID on all your devices to the same email address fixes this issue, and causes the syncing to begin working automatically. Here’s the step-by-step:
That’s all there is too it! We hope this works for you. I’m not sure why Apple chose to control the iMessage syncing in this way, but for those of you that have been having trouble, this works like a charm.
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