Wireless Cellular Data Services?

Swannie asks: "I'm an IT consultant who is on the road a lot. Unfortunately, it's the nature of security in today's enterprise that I rarely have a client that will let me access the internet, and usually not even attach my laptop to their network. Obviously, this leads to a problem in accessing my email... a big problem. Typically, the client will provide dial up lines, but all to often those go through their PBX, which typically limits me to 21.6-28.8k... ugh. Recently, I've been researching cellular data cards, and various services. This seems like the best solution for my problem. I'm looking for something that's reasonably fast, has an 'all-you-can-eat' plan, and inexpensive. Unfortunately, I'm going to probably have to pay for it myself. Since the client does provide a way to access the internet (dialup), it gets seen as a convenience, so cost is a factor. What experience have you had with services from companies like Verizon, AT&T, T-Mobile, NexTel, and Cingular? Are there any other services that I haven't thought off (unfortunately google searches for 'wireless internet' or 'wireless data' just turns up a whole lot of crap)? Any other advice?"

"So far, these are the options I've found:

• Sprint PCS: They have an all you can eat plan for $80 a month on their 'PCS Vision' network. They quote speeds similar to ISDN. Sounds cool, but I've had a sprint phone in the past and wasn't to thrilled with the service, and the price is a bit high.
• Verizon: Their express network plan is similar to Sprint PCS's offering... again, too much money!
• AT&T: They offer data cards on their mLife network (which is their GSM network IIRC). I didn't see anything about their speed, however, and they don't offer an unlimited plan... darn.
• T-Mobile: These guys actually have a decent priced unlimited plan at $29.00 a month. BUT, it looks like their speeds are limited to around 56k. I'd really like more speed, but I suppose that's the trade off for the cheap price.
• NexTel: I currently have a NexTel phone, and I really like it... had it about 2 years. They offer a data cable for it, which I tried, but I only get dialup connections at about 9600bps (yuck). They also offer a data card, and an unlimited plan which IIRC is about $56.00 a month, and limited to 56k... might as well go with T-Mobile then.
• Cingular: I couldn't really find a whole lot on their web site, it doesn't look like they offer a PCMCIA-card based data service...

Some more details, I live in Chicago, and usually my travels take me regional, so it would be nice to have a plan that allowed me to roam (all of the above do). I run Win2K on my work laptop, but I also have a Linux partition so suggestions on cellular PCMCIA cards that work with both, would be appreciated."