In theory, Apple’s iMessage service sounds wonderful—the ability to send and receive texts to/from people from your iPad or iPod touch as well as your iPhone is great. But you have to set it up a certain way to make that happen.
By default, iMessage on the iPhone defaults to using the device’s phone number—but as long as friends and family continue messaging that number, those messages will never go to your other devices. In order to make that happen, you need to make sure your Apple ID is also set up for iMessage on all your devices, then tell folks to message you using the ID, and not your phone number—new messages should then start arriving on all your devices, letting you respond from whichever is the most convenient.
Oh, and one important note: if you use your phone number for iMessage, Apple does some sort of device ID/SIM authentication that could leave that handset receiving your messages long after you’ve upgraded, even if you’ve wiped and restored it.
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