Make sure you have your email address set up as a way to send and receive. Your phone will (in my experience) default to the phone number and the iPad or MacBook defaults to email unless you let it use the phone number as a method of contact.
iPhoneMommy
"Be nice to people on your way up because you'll meet them on your way down." - Wilson Mizner
I have imessages both to my phone and my ipad,in my phone i have my phone number and my email address in Send and Receive...in my ipad as it is wifi only i just have my email address,does that help?