All credits of this hack goes to electron73 from THIS post.
Thanks to DrDrrae for the CWM zip
This will remove all entitlement checks on the native wifi hotspot app and will enable the native Bluetooth tethering option which was removed by at&t.
1) 3G Flyer
2) S-Off (get yours from Alpharev soon!)
Using root explorer or your favorite text editor edit the build.prop file under /system/build.prop and edit the following lines:
This is 100% stock ROM for the GT-P3113 (US WiFi version).
You can restore your tablet to 100% stock with this if needed.
1) LP5 MODEM: http://18.104.22.168/mexicet/MIDNOTE3.0_MODEM.zip
2) MIDONTE 2.1 BASE: http://22.214.171.124/mexicet/MIDNOTE2.1_BASE.tar
3) MIDONTE 3 KERNEL: http://126.96.36.199/mexicet/midone3-kernel.tar
4) MIDONTE 3 (Step 7): http://188.8.131.52...
Please note that i am not responsible if you brick your Galaxy Tab.
This worked for me and i now have a Galaxy Tab, on At&t making calls + 3G data + 850/1900Mhz WCDMA enabled.
**please note you need to have a SIM card with a proper voice plan ...