This is a personal annoyance of mine. Everything involving a serial line is preceded by "sudo stop modemmanager". Given that we're talking about a free desktop things should not have to require that.
I've just noticed and read the "Ubuntu Loves Devs" effort and I think that's something that could be addressed, or at least acknowledged. I've filed a bug report about what could be made to make modems and embedded / specialized development tools be less at odds with each other.
If you're interested in embedded development boards or accessing various devices using serial lines I'd like to invite you to join the discussion.