You cannot use that BlackBerry with Verizon.
Verizon uses CDMA, Nextel uses iDEN, SprintPCS uses CDMA, and T-Mobile, Cingular/ATTWireless use GSM.
Now, had you purchased a GSM Blackberry, unlocked, you could pick between Cingular and T-Mobile, but the CDMA providers usually don't let you supply your own equipment, because they suck like that.
Nextel is very limited to a handful of handsets that work with their goofy network.
Nextel does, however, have good coverage up and down Maryland and into DC/NoVA. The Nextel offices in Reston VA, for example have excellent coverage
If you want to use Verizon, you'll have to buy a Verizon BlackBerry, and the only BlackBerry that does Push-To-Talk are the Nextel models.
And that is one of the things I thank God for every night before falling asleep.