I just want to share what I did to enable MMS and Tethering automatically on SMART/SUN SIMs. By using these hack, settings will be automatically loaded just like when you insert a Globe SIM. However, I've only tried this on a factory unlocked Iphone 3G (Jailbroken). I think this will also work on software unlocked iphones. If you are not sure of what you are doing, I suggest not doing this.
Things needed:
1. Jailbroken, factory unlocked iphone 3g (V3). It should work on software unlocked phone but I haven't tried it.
2. OpenSSH installed via Cydia
3. winscp (windows). Im not sure on mac.
4. winzip or winrar app (windows)
5. CarrierBundlehack.zip file attachment
Instructions:
0. If you are using a custom profile that you got from
help.benm.at/help.php, you should remove it first to avoid conflict. To remove it, goto Settings, General, then scroll to the bottom and look for the Profile. Click it and choose remove.
1. Unzip or unrar the attachment to a folder. It should contain
Smart_ph.bundle and
Sun_ph.bundle folders.
2. Using winscp, SSH to your iphone (root/alpine) via WiFi.
3. On winscp's right panel, goto to ./System/Library/Carrier Bundles folder, and on the left panel, goto the folder where the Smart_ph.bundle and Sun_ph.bundle folders are located.
4. select the two folders on the left panel and copy them to the right panel, after which making sure the folder's permission is
0755 and the file's permission is
0644 (should be by default).
5. Now, you have to create a
symlink for the folders. Still working on the right panel in winscp, left-click on the
Smart_ph.bundle folder, then on the upper left part of the winscp window, click Files-New-Links, a window will open, then place
51503 in the
Link/shortcut file typebox, then make sure the
Smart_ph.bundle folder name appears in the
Point link/shortcut to. Next do the same with the
Sun_ph.bundle folder, but put
51505 instead and make sure
Sun_ph.bundle folder name appears in
Point link/shortcut to.
6. Once done, reboot the iphone then check in the Settings - General - Network. Internet Tethering should be there now. If you click on Cellular Data Network, you should see 3 settings; Cellular Data, Visual Voicemail, and MMS. All settings should already be there. I'm not sure why Visual Voicemail is appearing but if you're concerned about it, just remove the preset APN.
If you put a SUN SIM in your iphone, Network settings will be loaded automatically and you can use internet and tethering right away. But before you can use MMS, you need to reboot your phone first so that it will use the new MMS settings that were loaded.
USB tethering works on windows. However, I haven't gotten the bluetooth tethering work on windows. I haven't tried them on my mac yet (wife uses it with Vista installed hehe).
Note: These settings are only for postpaid SIM (Sun that uses minternet) as APN. If you have other SUN SIM, you can try to edit the APN for Cellular Data. This should work on pospaid and prepaid Smart SIM.
Forums 
This tutorial will be very helpful to those wanting to enable MMS and tethering to their 3G iPhones only. Can you please post some pictures of the tutorial and the units on Smart and Sun postpaid for the benefit of our users?
