Currently Being ModeratedAug 26, 2012 7:35 AM (in response to 4wheelgirl)
On your iPad, go to Settings app, select Messages. Check that iMessage is turned on.
The 'Receive At' address should be your Apple ID email address. If not, change it to be that.
On your iPhone, also go to Settings, Messages. iMessage should be turned on there too.
Scroll down to 'Receive At'. The default will be your phone number. You need to add your email address.
For messages to sync, this must be the same email address as your iPad, i.e. your Apple ID email.
In 'Caller ID', set this as the email address, NOT your phone number.
Try sending a message to a friend (who has iMessage enabled) from your iPad, then send a message to them from your iPhone. (Some users suggest first deleting any previous message threads from this person, other say it won't matter either way. I did delete mine first.)
When anyone with iMessage sends YOU a message, they must choose your email address (your Apple ID one) to send to, not your phone number. (i.e. in Contacts on their iPhone for example, they should add your email address there if they don't already have it entered.) If someone from their iPhone sends you a message to your phone number for example, it will only appear on your phone, not on your iPad.
Currently Being ModeratedJan 6, 2013 1:21 PM (in response to JDfunky)
My iPad and iPhone used to both work off of my cell number. Why do they not anymore?
Currently Being ModeratedJan 6, 2013 3:25 PM (in response to Douglas295)
Using FaceTime http://support.apple.com/kb/ht4319
Troubleshooting FaceTime http://support.apple.com/kb/TS3367
The Complete Guide to FaceTime + iMessage: Setup, Use, and Troubleshooting
Troubleshooting FaceTime and iMessage activation
iOS: About Messages
Set up iMessage
Setting Up Multiple iOS Devices for iMessage and Facetime
FaceTime and iMessage not accepting Apple ID password
Unable to use FaceTime and iMessage with my apple ID