The Mobian Bookworm has landed
blog.mobian.org
blog.mobian.org
In Phosh, the MMS server settings are store in Chatty rather than with the APN settings in the Network section of the System Settings app like in every other operating system.
And since Chatty only supports using one APN, if you switch APNs, MMS stops working. On normal OSs, you can set an MMS server for each APN separately. On Phosh, you can only do MMS on one APN.
But battery life is a function of both OS and hardware. So this question really doesn't make any since.