iSymon,
ok. so the situation for me is that i got a sim-unlocked iPad3.
I use this in Japan, and we've got couple of data only plan SIM's in market.
As mentioned on earlier on this thread, MVNO - bmobile/bmobile-aeon/dti etc etc.
When we insert the SIM, and enter the APN for 3G, it works.
Though entering the APN info on the tethering section is not retained.
it disappears after going to another screen. so the Personal HotSpot did not work.
I happened to bump into unlockit.nz, and downloaded the .profile and i got the Personal Hotspot option. this was for bmobile carrier. I moved on to using DTI, so i used apple configurator to create a APN setting. Whoalla, it worked.
let me know your setting required for APN and create a profile. if the setting has explicit userid/password, you might not want to discuss it here (publicized).