You won't be able to receive SMS Text messages on your iPad. You will be able to receive iMessages to both devices but this is something different to text (SMS) messages sent on your iPhone. iMessage is essentially Instant Messaging between iOS devices and compatible MacBook Pro systems running OS X Mountain Lion.
Why do you need to keep the same Apple ID? I suspect it is because you want to share apps without purchasing them again?
If so, the Apple ID and iTunes account are two separate things.
Read this to see how to use multiple devices with a single iTunes account. Set up the devices using one iTunes account but separate Apple IDs so you can each have your own iMessage and Game Center accounts.