I run the phones for a shop of 25 people.... I'm sold on Nextel.
Excellent customer service, reliable phones with good voice quality.
They also have "unlimited free incoming" plans, which works out well
for my people.

On the downside, looks like Nextel will soon be SprintTel, and things
will then be completely screwed up beyond repair.

A good way to do some research on the net: Search for "Sprint sucks",
"Nextel sucks", "TMobile sucks", etc. There are nightmare stories about
all the carriers, but in my experience, Sprint has always had the worst
coverage/quality/customer service in the world and known universe.