Yes I have synced the phone with the TM sim in it also reset network settings and even changed the name of the phone and it's still not there. It was working yesterday when I was on Meteor before the number ported. Now when I go settings\general\network there is no personal hotspot tab.
I had the same issue until I found this post, on an unlocked iPhone 4 originally from another Irish operator, new TM prepay SIM, new number (not ported). I had tried everything, including a wipe and setup as a new iPhone.
Adding the APN to the Internet Tethering section caused the Personal Hotspot option to appear.
(One thing worth noting is that the option didn't appear immediately, I had to go out of the Network page and go back in before it showed. Similarly, deleting the APN removed the option, but that wasn't immediate either).