try nextel...
It's not for everyone because their coverage can be somewhat limited in certain areas (click on their site at www.nextel.com and look for <coverage>, I've found it's pretty accurate). Their phones only work on their network (i.e., no dual-mode or tri-mode phones are available). Their National Business Plan is no roaming, no long distance anywhere in the U.S. you can get a signal. Not sure about their rate plans outside of the midwest, but I think I pay something like 199.00/mo for 2300 anytime/anywhere in US minutes. For an extra 10 bucks/mo you can get unlimited usage after seven (I think) and weekends from Friday evening to Monday @ 8:00 a.m.
Their phones also have that internet deal and I think you get basic access included in the National Business Plan (although I'm not 100% sure of that).
I forward my office and home phones to my cell when I'm out and it works pretty well (self-employed and my only employee is me-also why I have such a high minute plan). In the now almost three years I have had their service, I have been unable to get a line maybe 20 times (and that was almost always in south Florida/Miami Beach area during Februrary (peak season) - the one exception was in LAS during one of their biggest conventions of the year).
Finally, if you fly internationally (I don't), I think you can get their i2000 phone that will apparently work in many countries (especially, Europe, Mexico, parts of Asia and SA). I'm sure it's outrageously expensive per minute but the idea of forwarding to one phone number to reach you anywhere in the world is kinda cool (and not have to use an Iridium satellite phone or something bulky - and probably very expensive - like that).
Hope this helps.