• Sprint’s dual mode U301 USB modem (left) supports both WiMAX and EV-DO. Sprint’s 3G/4G Mobile Broadband Plan costs $69/month (on a 2 year contract), but includes both 3G and 4G data access. It works on both Macs and PCs.
• Cricket Broadband costs $40 a month with no signed contracts and no overage fees. It uses Sprint’s CDMA network and their coverage map shows similar coverage to Sprint. Cricket’s A600 Modem, also with a microSD storage slot, is free with a new activation. It provides 3G (EVDO Rev A) & 1X speeds, and the $40 per month service is capped around 5 MB per month.
• Virgin Mobile’s 2Go plan has prepaid 3G data, but their $60 plan only provides 1GB per month. Virgin’s $99 Modem, a Novatel Wireless MC760 has an optional external antenna for enhanced performance on the fringe areas of networks and works with Macs and PCs.
• Millenicom has an unlimited prepaid data option for $69.99/month. It requires the purchase of a Sierra Wireless 598U modem for $99.99. The unlimited service is for personal and family use and is not to be used as a public WiFi, broadcast to multi-dwelling units. Their BYOD (Bring Your Own Device) Account works with mobile WiFi routers such as the Novatel Wireless MiFi 2200 mobile router which costs $298 at Amazon (without a service plan). It works over the Sprint mobile broadband network. The standard Millenicom Mobile Wireless Broadband account, with a 5-gigabyte usage cap, is $59.99/month, along with a one-time fee of $49.99 and a $15.00 shipping fee to get the account started.

From: http://www.dailywireless.org/2009/12/30/prepaid-data-plans-cheaper/