Receiving mms on AT&T network

[nukeemaway]

Good morning everyone. I was led here by some of pizzaboy's posts while googling for a solution for my problem. I went through a number of the posts on this forum and did not see a solution to my problem, although I know very little about phones and so apologize in advance if it already has been answered.

I had an old AT&T slider phone from Samsung which still works but the screen seems to have blown (so I've pretty much lost everything on that phone unless I can get it repaired). I was due for an upgrade, but apparently now AT&T only offers garbage phones unless you get a data plan.

In the meanwhile, I was given an unlocked LG Fathom as a holiday present. I was able to switch it to gsm mode and installed the media net settings cab (which I believe I got from a pizzaboy post). I also installed the PHM registry editor, if that will help.

I have two issues with the phone:
1) Every time someone tries to send me a picture text, I get a "message not found" notification from my number. I can send picture texts no problem.
2) I was able to get my voicemail by changing the voicemail number from *86 to my cellphone number, but even after deleting the messages, I continue to receive the notification on the home screen about having (nonexistant) voicemail messages. Additionally, after checking my voicemail, I seem to be getting a blank text message from a symbol that looks like an elongated plus sign/cross.

I've already wasted so much time trying to solve these issues; if anyone can help me it would be so greatly appreciated.

Thank you in advance. Happy holidays!