IPhone 3G S: Enable Tethering
theappleblog.com
theappleblog.com
http://forums.macrumors.com/showthread.php?t=714535&page...
http://www.enabletethering.com/Tethering.html
FYI, the APN field (whose default value is wap.cingular) needs to be replaced with the value of acds.voicemail. The article implied you somehow could have two addresses in there.
http://www.mydigitallife.info/2009/06/28/how-to-restore-and-...
"Worth noting is that some users have experienced trouble with their visual voicemail following this procedure. If you do have trouble accessing that feature, simply navigate to Settings → General → Network → Cellular Data Network and within the Visual Voicemail section add “acds.voicemail” into the APN field. Once that is done, you will be able to once again use your visual voicemail."