I just bought a Sprint PCS Vision plan and a Merlin PCMCIA PCS connection card. Basically, anywhere Sprint PCS is active, which is just about in every major metropolitan area, I can dial up anywhere on the road, with no strings and cables attached, literally speaking. It's costing me $100/mo, but I can VPN into our file server and check live inventory.
Data throughput is slightly faster than a dial up modem. Ping times are anywhere from 300ms up to 2 seconds, all depending on signal strenght. I live on the fringe of the PCS network, so I expect it to get better the closer I travel towards the center of town.
If you went with this or any other PCMCIA card, you are subscribing to new cellular service. The card has a phone number burned in, but it can't receive calls. I think Sprint makes some plans that allows the use of Voice traffic in addition to data traffic, but I'm not 100% sure which plans they have.
So far, I'm impressed with what I can do on the net. Bitmaps and large JPEGs do take some time to load, so do Java script and ActiveX components. But if all you are doing is capturing email, a smaller plan might do the trick. I've measured my data flow and with just 3 days of usage, I've exceeed my 80MB limit. Had to upgrade to unlimited plan before I had to pay an astronomical surcharge of so many dollar for every megabyte... .
Hope this helps... .
Martin