I also ordered a 7250 off of eBay and I use Alltel! What I found out was that since it is an internet ready phone, you HAVE TO HAVE a plan with internet capabilities. They cannot activate this kind of phone soley for...just being a phone (or just using it as a PDA). Since you have Alltel, you'll need to get a Smart Plan which is what I did. The plan I got is $89.99 for 500 daytime minutes and unlimited everything else (texting, internet, 7PM nights and weekends, mobile to mobile) and plus you'll get My Circle. (10 lines to talk to for free)
But yeah, there's no way to have it activated without getting internet. I wanted to do the same thing but now since I have unlimited internet...I've been on it all day.
If you decide to get the Smart Plan make sure you get the PIN number deactivated. Alltel (and all the other providers, I think) have a BlackBerry internet site that you should register (but I don't know if it's manditory) BlackBerry Internet Service
. Since the previous owner probably registered on their BlackBerry site, you can't log in without the screen name and password. So, when you go back to Alltel, ask them if they can deactivate the PIN number so you can re-register on the Alltel site.
Sorry it's so long, but this is everything I learned this week because I did the exact same thing. I hope it helps!