Can't send MMS with 8520 and ATT
 

This is a unlocked t-mobile phone. I got it a few days ago. Have the BB plan with ATT, everything worked fine then I got some app error and couldn't fix it so ended up reeinstalling the OS and everything on the phone. Called ATT to have them reset something so I could get the service books from ATT again and get the MMS option. Got that. Internet and everything works, there is the MMS option now but I can't send pics now. I was able to do this a couple of days ago before I reset and restarted my phone, so I know it's not the phone-its some setting or att or something.. I looked everywhere, in all forums and looks like all my settings on the phone are correct.
I'm not sure what my next option is? I don't think calling ATT will help bc they don't know what to do-the first time I called them they couldn't figure out and had no idea what service books even are... but somehow the MMS did start working after the BB plan was actived- but not this time around.

What are my options now? Just resent the OS and phone again??
Yes I did delete the MMS service books and reregistered with att-got them again-still nothing..
Just has a red x on all the mms sent.

=(
I'm starting to really not like BB

Look in your Service Books and delete the current two MMS entries.

Reboot your device with a powered on battery pull.

Resend the Service Books again. You can do it from your personal email setup on your device, login > Help, Resend service books.

What do u mean by using email to reload service books? And log into what?

Same problem with my unlocked T-Mobile 8520
 

Cannot send mms.
T-Mobile has their own mms settings installed and users do not have access to them to change them.

Has anyone found out how to fix this? I am thinking it will require a flashing of some sort to change the settings to AT&T/CINGULAR.

You have THE BlackBerry Data Plan from AT&T?
You'll have to have it for MMS.

Try going into your TCP/IP settings (Options > Advanced Options > TCP) and set them for your carrier: What are the TCP and APN settings? - BlackBerryFAQ
(For AT&T use Cingular Orange)

Yes that's all well and fine for the internet/browser, but what user b.olga and I are saying is that the MMS still doesn't work. We cannot send or receive pictures/videos/sound files.
The mms setting are inaccessible to the user, and they are set to t-mobile since these are unlocked 8520's.

I didn't need it with my 8320.

If the TCP/APN settings for ATT don't get your MMS working, from ALL that I know, you will need the BlackBerry Data Plan on your account to enable the MMS.

When it is provisioned on your account, you can access it from your device at the icon named "Persona Email Setup".

To send and receive mms, phones access the internet/media net/web for a few seconds. The usage is so small they don't charge you for it. I currently have the pay-by-use web on my account, so I don't need to add a data plan.

Tried the above steps (deleting both MMS entries, battery pull + service books) on my VZW 9550; still can't send MMS, but can still receive them.
I'm done Googling & trying for the past two months.