SIM 800? SIM 900?

I have had a SIM900 GPRS shield for some years but I have never used it, and I recently assumed it was obsolete because it is (probably) 2G. To make matters worse, I kept thinking it was a SIM800, but I now realise it isn't.

Is the SIM900 shield good to go on a 3G network?

I ask now because I have a spare 3G SIM...