When initially trying to activate iMessage and Facetime on my iPad, I had a problem with being able to access my phone number. When I signed into my account (on my iPad), I actually wasn't even presented with the option of a phone number - notwithstanding the fact that I was contacting others (and being reached by others) by my phone number on my iPhone. Having both the iPad and the iPhone on, I kept trying to turn off and on both iMessage and Facebook in "Settings" on both my iPad and iPhone, hoping that that they would eventually sync. But this proposed solution by others was unsuccessful for me.
So: I was able to send & receive messages (as well as contact others via Facetime); in "Settings", my "Date & Time" was "Set Automatically" to "On"; and I even tried to turn off the Wi-Fi and sync via Cellular Data only. None of these proposed solutions worked.
Then, I found out what the problem was: When my iPhone was originally activated, it automatically registered my phone number for contact purposes. But I was using iMessage on my iPhone for quite some time without actually being signed into my Apple ID account. When another device - such as an iPad or iPod - is being used for iMessage or Facebook, you are prompted to sign into your Apple account, using your username and password. These two devices will not register your phone number as an option for contact unless your iPhone is signed into your Apple account as well. In other words: your phone number will not be synced.
Go into your "Settings" on your iPhone and click on "Messages". Scroll down and click on "Send & Receive" (which should be followed by your phone number). On the next page, you will be able to determine whether or not your iPhone is using the Apple ID for messaging purposes. (Note: This information applies for Facetime as well.) If it is using your Apple ID for messaging, than at the top, you will see "Apple ID: <your particular e-mail account>" in Blue text. However, if you are not using your Apple ID for messaging, than you will see the words: "Use your Apple ID for message". Even though below this you will see your phone number checked as the contact source, you will want to click the tab that says, "Use your Apple ID for message". Sign into your account (just as you must sign in for iMessage on your other devices), and just choose your phone number as the "Send & Receive" contact. (The option of the e-mail will be there too, but you don't have to check it. And later on, you can delete it as an option.)
Now that all of your devices are signed in using your Apple ID, the other devices should register your phone number as a choice. It may take a little while, however. What I did was sign out of iMessage on my iPad, and then sign in again. If the option didn't appear, I just went back and signed in again, and kept doing this until the option for the phone number appeared.
Again, this will work for Facetime as well. The solution is to sync your iPhone account with the other devices by using your Apple ID for messaging (and Facetime) purposes.
