Install commcenter patch http://mir.cr/SFR7CWDC
Create custom ipcc http://www.volkspost.info/ipcc_fw3/
Rename ipcc to zip. Extract contents. Open Payload\carrier.plist with text editor or plist editor. Add the following code at bottom before the last </dict>

<key>signature</key>
<data>thisisafakesignaturethisisafakesignature</data>

For tehering, hotspot & MMS add the same code before every <key>type-mask</key> in the plist.
Change type-mask key to 1,4,48. Type-mask = 48 for tethering, type-mask = 1 for data, type-mask = 4 for MMS

For Facetime add

<key>PhoneNumberRegistrationGatewayAddress</key>
<string>+447786205094</string>
<key>RegistrationOptInRequired</key>
<true/>

Save the file.
Replace png images with your custom ones. Add @2x to the filename.
Re-zip the package. Rename to .ipcc

Prepare itunes On a Mac open the application Terminal (in Applications/Utilities) and type:
defaults write com.apple.iTunes carrier-testing -bool TRUE
on Windows open command prompt and type:
"%ProgramFiles%\iTunes\iTunes.exe" /setPrefInt carrier-testing 1

Apply the ipcc file to your iPhone
Click on the iPhone in "Devices" (left program bar)
On Windows shift-click "Update", on Mac option-click "Update" (NOT "Restore"). iTunes will pop up a dialog, selct the downloaded .ipcc file and click "OK". iTunes will "update your carrier settings".
Disconnect iPhone and PC, shut down the iPhone (red slider) and restart it - thats all!