rotohammer from xda has released instructions for T-Mobile Modem Switcher for your Samsung Galaxy Tabs. With this, you can either 3G or Phone and 2G that you need to. The hacker posted the instructions last year in December and assured that soon he will be releasing an app for the same. But the time he is unable to make the app, he asked to follow his instructions that he would be clubbing into the app.
Don’t know whether the app is still available or not but yes the steps to do the same are.
Modem Switcher Instructions
1. The first step is to install GScript Lite from Market. It helps to run and load the shell scripts from within the Android using a single touch.
2. Next download and install BusyBox Installer. It installs a working version of BusyBox on your phone. It is needed by many root apps and is a must tool to have.
3. Download modemswitch.zip file. Comment here if you want it in email. Make sure that this zipped file contains the following 5 files in image.
4. Extract the contents of the above zipped file onto your phone’s SD card.
5. You will see that there’s a directory /sdcard/modemswitch having all the 5 files in it.
6. Copy the /sdcard/modemswitch/switch.sh to /sdcard/gscript/ directory.
7. Open GScript.
8. Press ‘Menu’.
9. Press ‘Add Script’.
10. Press ‘Load from file’.
11. Select the switch.sh file and press ‘Save’.
12. Hold the desktop. Select ‘shortcuts’, then ‘GScript Lite’, followed by ‘switch’.
13. Disconnect the USB and/or unmount /sdcard.
14. Finally you need to press the ‘switch’ desktop icon for switching the modems.
15. Samsung Galaxy Tab will reboot with effect of new modem.
All supports at hackers thread