well, actually, no. the sierra card you are referring to is actually designed on a similar sort of principle, but instead of working just in your house - it works anywhere your cell phone does - it has a much wider area (3-5 miles per cell phone tower). however, speed gets sacrificed - it's usually about the speed of dialup.

so wifi and cellular are different...and then there's the differences betwee GPRS and CDMA 1RxT but I think that's a convo for another day