My phone is attached to an apple id, I believe this is how I pay for apps. How do I check if my number is attached to an apple id?
My phone can send and receive iMessages.
The rumor is that the release of iOS 6 and OS X 10.8.2 will allow Macs, iPads, and iPod Touches to receive iMessages that are sent to your phone number. As of now, the only device that will receive iMessages is your iPhone. However, you can still send messages to phone numbers from a non-iPhone device (although as stated previously, these messages are through the iMessages protocol, not SMS, and thus they can only be received by Apple devices that support iMessage).
To check what email address(es) your phone is receiving iMessages at, go to Settings > Messages and scroll down a bit. You should see a button that reads "Receive At" and then it will say some number of addresses. Tap on it. Your Apple ID will be displayed, as well as your phone number. If you have other email addresses that you'd like to use, you can go ahead and add those.
One other thing to note on this screen. If you have multiple addresses that you're receiving at, "Caller ID" will be displayed at the bottom. This doesn't affect phone calls or normal SMS text messaging, but it sets what people will see when you send a message through iMessage. By default, your iPhone's phone number will be the caller ID (and on your Mac, iPad, etc., it will be your Apple ID email address). Setting all of your devices to the same caller ID can help to ensure that messages will be received on all devices, because messages sent from the iPhone with an email address as the caller ID will then be replied to at that email address (which all devices have access to). Granted, if people send you a message to your phone number, then only the iPhone will receive it (at least, at this point in time). The caller ID setting does not affect what address or phone number you receive messages at - it only affects what other devices will see you as (and reply to).
I hope that wasn't too confusing, and that it helps.