Messages
How do I set up my iPad & iPhone to continue message conversations?
iPhone 3GS, Windows 7
Have IPAD and IPHONE set up by email address under Messages. Your phone by default using your phone number, you can add the same email address associated with the IPAD on your IPHONE under Settings - Messages -Receive At then select USE YOUR APPLEID FOR IMESSAGE.
This will have your conversations sent to both devices.