OK so i have found a SOLUTION to this problem that worked for me. I hope this works for others. I have a Verizon Galaxy S5 with a t-mobile sim in there. When i first put in the settings that everyone was giving me, Calls, Text and Internet worked but i could not send/receive MMS/Picture messages. Here are some settings i found that worked: (I am talking about adding a new Access point name)
Name: T-Mobile US LTE
Proxy: Not Set (leave blank)
Port: Not set (leave blank)
Username: Not Set (leave blank)
Password: Not set (leave blank)
Server: Not set (leave blank)
Multimedia message Proxy: Not set (leave blank)
Multimedia message Port : Not set (leave blank)
Authentication type : None
***NOW THIS HERE IS THE IMPORTANT PART I HAVE FOUND THAT WORKS. ADD IT EXACTLY LIKE BELOW, NO SPACES****
APN type: default,mms,supl,hipri,admin,mobile
APN Protocol : ipv4/IPv6
APN roaming protocol : IPv4
Mobile virtual network operator type: None
press the menu button and click save. Try to send/receive an MMS/Picture Message.
Thank you, 1-800-gio, that worked. I've followed purported solutions from various websites, including the usually-reliable developers, but none solved my problem. One thing to note for others who may find this: I also deleted the other APNs that were already there by default.
I have a similar situation, cannot download MMS pictures, but with an AT&T Galaxy S5 Active, and in Alaska on GCI network. Those APN settings do not fix the problem, and only allow for emergency calls...