Prepaid carrier Virgin Mobile will be introducing a Novatel MiFi router next week, the company told us after the device appeared at a Best Buy summer preview event this morning.Virgin Mobile's MiFi, like the models available for Sprint and Verizon Wireless, is a slim little router that turns 3G signal into a Wi-Fi hotspot for up to five devices.Since this is Virgin Mobile, this MiFi will be entirely prepaid - $149 for the device, and then anywhere from $10 for 100 MB to $60 for 5 GB. When you need more data, you can re-up. (Virgin has a full chart of their data rates on their Web site.) Activation is simple and there are no activation fees; you can top up your account with credit or debit cards, or Virgin Mobile top-up cards bought at local retailers.