A big announcement within the community last week regarding SMS, MMS over 4G for North American users.....
Good news! Over the last few days we enabled initial support for SMS & MMS on the Pixel 3a & 3a XL on US carriers. A bunch of other fixes made it into the current release candidate to perfect it but this is the big one.
SMS work reliably on 4G now and MMS partially work (lacking proper Group MMS support right now). The phone doesn't trip off the carrier with its incomplete IMS support too.
If you want to make sure you can reliably receive MMS please make sure your APN settings are compatible, either by changing the settings or, if the system-settings GUI doesn't work, by editing the /var/lib/ofono/<number>/gprs file manually, or by disabling the Internet APN completely. Staying off WIFI is also reported to work reliably
Find the original post and more details here.
I'm willing to test and work with anyone to polish up this feature, if you need to get ahold of me please find message owowow#1153 on Discord or email@example.com.
See also MMS Infrastructure.
Update on September 8: