Regarding 3g speeds, I'm using 3g to post to the forum right now, and have been for months, off and on, along with wi-fi to broadband.
Currently, VZ and Sprint, I believe, run EV-DO both for laptop data cards (like my VZ), and to cell phones. There are 2 tiers of service, with the fastest sevice available only in Metro areas. There you can get ~700 kbps steady throughput on downloads, although the ~400 is much more common. Uploads poke along at ~100, although the new rev of EV-DO is supposed to be much faster on the upload, closer to the download speeds.
Outside of metro areas, and pretty much ANYWHERE you get cell signal, you can get the slower tier of data service, where downloads move at 100-150 kbps, and uploads are 50-100 kbps. i want to emphasize the portability of this. All you need is a single "bar" of reception (or even less), and you have net access. That means 90% of the country, including checking emails while you drive down the highway.
I believe these speeds are the same for cellphones, you be the judge on whether that's fast enough to support a slim MC client for the phone.