What about something along the lines:

It's a slight variation of what tekojo suggested.

Some reasoning for coming up with this slogan:

• It sounds nice and friendly.
• It does not claim to be the only place where open mobile devices and software are discussed nor does it exclude particular topics. It is non-limiting and open.
• It does not limit the audience to developers/hackers but rather invites everyone with an interest in open mobile devices and software.

I think so far very interisting aspects had been brought up in this discussion. I also think that both platform and apps are equally important. One does not work really well without the other.
I also think that users are important as well. In my experience here, very often a user came up with some creative requirement or a great idea for a certain solution but lacked the skills, or time, or whatever to implement it. I got some nice inspirations for new applications, new features, or further development steps that way myself.