Jason: Jason im not sure where you are based but im sure the Vodafone 3G Network / dataCard would suit your needs.

They have several tarrifs, I personally manage around 60 accounts for my company and use two main tarrifs for the users.

1) Connect 200 (which gives 250mb of downloads)@ £35/per month additional MB priced at £1.13 per mb
2) Connect 1000 (1100mb of downloads) @ £88 per month (additional = 0.59pence per mb)

There are others though:

450mb @ 53.00 per month
75mb @ 23.00 per month

The beauty of the G3 network is if you are in a G3 eabled zone you get connection speeds of upto 370k as opposed to the standard 56k of normal GPRS coverage.