We don't have a land line either and haven't for over a year. We use Cingular as it's nationwide and we do a lot of traveling (and recently, moving). We pay $80.00 a month (taxes and fees included) for two lines and I *think* 1300-1500 minutes, can't remember exactly. Includes call waiting, caller id, and a bunch of other features we never use (not text messaging, but we don't use that anyways). I cringe when I think of $80.00 a month, but we use a lot of minutes as we're close to our families and talk to them A LOT. The nice part is, Cingular does do rollover, so we have never been charged for going over our minutes. Some months we go over, others we go under, but we never have to worry about it. Also, if your friends/family are in Cingular's network (none of ours are, hence the reason we had to get so many minutes), you talk free all the time.
I'm definitely not trying to sell you on Cingular, but rather compare different companies, prices, and features and decide what is best for you.
I hate the fact that we are so reliant on cell phones and we are paying almost $1,000 a year on them, I feel so mainstream in that regard. On the flip side, they are so nice to use in emergencies and you can't put a price on keeping in touch (well, I guess $1,000 a year
).