it's pretty obvious, for cingular
pro:
fancy new phone for free or at affordable price, especially nokia phones.
unlimited weeknight and weekend.
some gsm900/1800/1900 triband phones for europe/asia travel.
get new triband phones from europe/asia before release in us market.
bad:
expect system busy, drop call at weeknight prime hours.
it's almost completely no signal in most parts of temple city, san marino, or around dense apt.
nextel is for business use, too expensive for personal use.
you need to get all your friends onto nextel boat to use the walkie-talkie feature.