Yes, I the Airrave is only for 3G.
As for the cost, Sprint had waived the monthly fee. They issued the device when the local tower was down for a month and damaged by a powerful storm during the spring. They did tell me I needed to returned it when and if I canceled my plan, otherwise they would charge me $150 for the device. I decided to keep the Airrave and now have it at my weekend home in the Catskill region of NY. Since Sprint does not cover the specific area where my home is and they recently put a cap on roaming, now I can use my phone without worrying about usage issues.
For those with performance issues with the device, you can adjust the power levels via your online account. You would click on "manage device" and from there you can set the power level from low to high. You can also restrict specific phone numbers that can use the Airrave, otherwise you will be sharing the Airrave that is within coverage of the device.
Hmm, I don't see any options on my online account to do such a thing. Any further instructions on how to access these features?