First this is the only way I could get mms to work after hours of email with net10 and retyping settings.
You will need root. I think you will need root since it is a system file you must edit.
Deleting apns does nothing in android there still saved in the master file. This file will need to be edited it is easy and you can keep all the other settings in it if you want. I did no harm.
First net10 and straight talk are the same settings for AT&t this should also work for t Mobil just use there settings.
Ok with root I used root explorer
next open the file system ETC
change mount to r/w
then hold down on the file apns-conf.xml
go down the list to open in text editor
this is all the settings for the apn you have on the phone from when you got it. now looking at the set up this is what you need to do replace the settings of one of the ones done there with the new ones from net10 or ST all new settings go between the " "
This is what it would look like when done
apn carrier="NET10" or you can use "Straight Talk"
Using the menu key on your phone save this.
Back to home screen settings wireless & network
access point names
using you phone menu key use the rest to default
for fun click on the one you redid it will have the name you used net10 or ST
you can not edit it so you can now go back to home and try to send a mms. You might need to restart your phone
You shouldn't need to do this if you setup the APNs correctly. If your unable to delete the stock APN(s), use APN Backup & Restore from the Android Market to delete them. Then create your new APN for ST and make sure you enter everything exactly as is. Then everything will work.
I did that about 20 times and it never took, I used apn backup and restore but it did not erase the main fail under etc folder. Also when I used it or the main settings to add a apn it worked for internet but not mms. It never made a xml file to replace the old one at all.
Heck net10 even sent the settings to the phone but they did not work.
This is a AT&T avail by zte might be something with there file system,
No, every you said there about the xml file not changing is how its supposed to be. On Android, the /system partition is read-only unless you root and re-mount it writable. The XML file holds the default settings, but that does not mean they are the current settings. When you change it, its saved in /data, not /system. So it overrides the default settings. If you delete the default APNs, they remain in the XML file so you can restore the default ones if need be at a later time. You can restore default APNs on the APN page by tapping the Menu key and then Reset to default. The reason user changes don't make it to the /system partition is that in case the user screws something up, they can just wipe /data and the phone is working again. Its very different from Windows where you directly modify the OS when changing things or installing programs. In Android, the system files are never touched (by default).
Several people on here use the Avail on ST without rooting and editing a system xml file.
I have MMS working on my Shap FX Plus without rooting.
EDIT: When you are done configuring the APN, do not press the Back button or your settings won't get saved. Press the MENU button instead and select Save. Not intuitive but that's how Android rolls for APN configuration.