I am using an iPhone Xs using software version 14.3. I cannot send a photo in Messages using MMS. I realized today that if I try to send a photo to someone that does not use iMessage, I receive a message the following message: "Cannot Send Message. MMS Messaging needs to be enabled to send this message." In Settings > Messages I have iMessage turned on, Send as SMS is turned on, and MMS Messaging is turned on. in Settings >Cellular, Cellular Data is turned on. I have tried Settings>General>Reset and have gone through the Reset Network Settings. I have tried turning off wi-fi, turning off iMessage, and several other changes and none of those changes made a difference.
If I am composing a message (using Apple's Message app), and I try to add a photo using the camera icon in the lower left of the screen, nothing even happens or opens unless I am sending a message to someone using iMessage (or at least the previous messages were in blue). So I cannot even attach a photo from within a message, unless I am sending a message to someone using iMessage. Then I can tap the camera icon and go to Photos and attach a photo.
I can send just a text message to non-iMessage users. I just can't atttach a photo or possibly another type of file. I also tried resizing my photo so it was only 23 KB and I still couldn't send a photo using MMS. I wanted to rule out that the photo was too big.
Is there a setting I am missing? Does Xfinity Mobile allow us to send photos using MMS using Cellular Data?
You appear to have all of your settings correct. I suggest that you turn off MMS messaging, power off then on, turn MMS messaging back on.
Please understand that both SMS and MMS use carrier cellular servers and networks (or WiFi Calling to indirectly connect to carrier servers) so they don't really use WiFi per se. Xfinity Mobile does require cellular data be turned on and does charge for data used for MMS. Xfinty Mobile has a 600kb MMS limit.
Perhaps you were trying to send an MMS to someone who had MMS messaging or their cellular data turned off?
I tried your suggestion (turn off MMS, restart iPhone, turn MMS back on) and it doesn't make a difference. I think it is more than someone having their MMS turned off, because I can't send MMS to anyone who does not have iMessages turned on. Plus, like I mentioned in my original post, I can't access my camera using the camera icon (see the camera icon circled in red in the attached image) unless I am trying to send a message to someone using iMessage.
So I keep wondering if I have missed a setting somewhere. I have tried turning on and off several different settings to see if it would make a difference, but I haven't seen any changes.
Unfortunately you may need to do the nuclear option. Backup your iPhone to iCloud, then erase all content and settings, then restore from your backup.
Did you ever add another app such as Verizon Message+?
I didn't see Xfinty Mobile or XM Mobile on your attachment? Also, LTE only had one bar?