Re: @Alienrat and ASAC
Looks like an excellent suggestion. Then you'll have to only pay for your bandwidth usage and server maintenance instead of somebody else and their app.
Something like phpBB with a mobile theme may work, and where you can also upload stuff to.
This requires investigation.
On the down side, you will be responsible for security yourself, and if you get pwned and all your private+client data goes walkabouts on the WWW....