Is this allowed?

[jsjaybone]

I just recent added a 3rd line to my account for my mom on my family plan. At the time I had an old m520 sitting in a box so I opted to use that instead of using my $150 credit for a new phone. I saw that the new Pre came out so I used my credit and got the phone for $199 moving the number from the m520 to the new Pre. I then signed a 2 year deal on that line. Now that I'm locked in can I now flip numbers between 2 esns? What I want to do is move my wife's number on to the Pre and move my mom's number on to my wifes Rant. Is this allowed since I did sign the 2 year deal on the Pre? Thanks in advance for your replies.