I JUST finally figured this out for myself on a lumia ICON from Verizon, on a Telus network in canada. I initially upgraded from 8.1 (with all mms and cellular data working), and upgraded to windows 10 mobile on the slow ring. I started on a new build, and then I realized i wanted to use a backup. So i hard reset. I had previously used this phone on windows 10, so i decided to use a backup from a couple months ago when i was last on windows 10 mobile. That's when i noticed that mms and data weren't working. I put in my telus APN settings, and my LTE data started working. No MMS still. I found this forum and did some reading, and was just about ready to do ANOTHER hard reset to try that route, when i decided first to try downloading the Access Point app and open it, knowing it will say that it's unsupported. I looked in the store, couldn't find it, so i did a quick search for a direct download of the Access Point app. That sent me to a direct link to the store, which worked and downloaded correctly. Waited for it to install, then hit open app. Got the unsupported message. Nothing seemed to have changed, but I decided to try it anyways. Turned off wifi for good measure, and first tried internet data connection. Worked. Then I tried going to messaging, then ... settings, made sure "Allow MMS if cellular data is off" (not sure if this is important to have on or not), turned on "MMS group text". Then I went to messaging app, and tried sending a photo to a contact. Usually when I send it, it takes two or three seconds before it vibrates at me and stubbornly says "try again". This time it didnt happen. I kept waiting. Seemed too good to be true! I sent a text asking if they got it. "yeah i did, why?" OH MY WORD FINALLY. They wouldn't understand my joy of being able to send a picture through text, so i didn't answer back. So yeah. Basically the moral of the story is that my MMS and LTE works EVEN THOUGH I SELECTED A BACKUP through setup. I'm actually typing this immediately after figuring this out, and something truly amazing just happened. I asked my wife to send me a photo through mms, and now I'm just thinking I'm a wizard or something, but i turned off my cellular connection, leaving Wifi on. Bzzz. I just got the picture, with data OFF. I guess that's what "Allow MMS if cellular data is off" is for in the messaging app settings! Thinking this may somehow be because my wifi is on, i turn that off and ask for another picture. IT WORKED. AGAIN. Data, and Wifi OFF, i'm now getting MMS, after configuring using a backup after hard reset, on windows 10 mobile build 10586.164.
Just incase, these are the Telus APN settings i used:
Profile Name (i don't think this matters) telus
APN: sp.telus.com
Username: leave blank
Password: leave blank
Type of Sign-in info: None (i had issues of trying to select PAP or CHAP, but the settings never stuck after saving)
Check on: Use this APN for LTE and replace the on from my mobile operator
Proxy Server: 74.49.0.18
Proxy Port: 80
Check on: Apply this profile
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