Which broadband provide can use Sprint broadband card?

My guess is only sprint.

First like cell phones these devices are locked to a carrier, you may be able to get a unlock code but it will unlikely help.

The biggest issue will depend on which type of broadband you are using from sprint. If it is based on CDMA maybe you could move it to verizon. More than likely it is WiMax. Sprint was first to market with this technology and nobody else other than their partner Clear uses it. Everyone else in the world appears to be going for LTE. Eventually you "should" be able to move devices between say ATT and Verizon both who are implementing LTE networks even though their 3g systems are incompatible. Most other carriers are also going LTE so I suspect there will be very few that choose to go WiMax.

I thought sprint offered prepaid. I know they have to only true unlimited data plan. You could also try clear since they are sprints partner but if i remember right sprint had more plans.