I kinda figured out a way around the text messaging on the 7520. What I did was to create a gmail account that forwards directly to my 7520. All nextel sms users can send to a phone number, or email address. My wife can send to the gmail address from her I830, and I can reply directly back to her using her nextel sms email address (what nextel didn't tell us) the sms address for nextel phones is:
(replace 5555551212 with the number you are text messaging) this works great for us.
If anyone else wants to try it out, PIN me and I'll set up a gmail invite for you. Make sure you send me your name and email address to set it up.