It absolutely DOES NOT need WiFi or Cell service. Neither does my Infuse, my iPhone 4, or my iPad 2 (GSM model - the WiFi iPad has no GPS chip AND ONLY USES WI-FI for GPS).
These devices all have dedicated GPS chips in them and the WiFi or Cell connection only enhances or assists (A-GPS) the GPS chip and can sometimes make your GPS lock faster.
If the GPS in the SII is as bad as the one in my Infuse (and I understand it is NOT) it might take forever to lock without WiFi or cell but right now I have turned off WIFI and CELL on both my Infuse and iPad and went into my backyard and I am able to lock the GPS on both devices. The iPad took 8 seconds to lock and the Infuse over 3 minutes. iNFUSE gps IS crap.