A lot of people are not able to edit the APN settings on their iPhone 4. Here’s a quick guide on how to do it on a jailbroken iPhone 4 running on iOS4.1.
1: Go to Cydia and search for Supreme Preferences 3.0 and download it.
2. Once installed, go to WinterBoard.
3. Tap on Select Themes.
4. Select Supreme Preferences 3.0.
5. Go to Setting > and select Supreme Preferences 3.0.
6. Tap on Applications.
7. Select Phone and change Cellular Data Editing to ON.
8. Now Cellular Data Network appears and you can tap on it.
9. Now you can change your APN Settings:
Note: If you replace with a new SIM card, repeat from Step 5 onwards.
i have iphone 4 on 4.2.1 with baseband 1.59.00 jailbrroken with grrenpoison and unlocked with ultrasnow. but am unable to use gprs and hence followed this post and downloaded and even selected the theme. but am unable to find it in settings. help plsssss