Media mailing problem: solved.
The resolution turned out to be easier than imagined, and could be easily handled with dyndns' webhop redirect feature -- no Postfix hackery required. So, you can now email photos and videos right from your phone to the address assigned you by the social network, say, firstname.lastname@example.org (notice that it's @feedmeshow.ning.com, not @feedmeshow.com).
Oh yeah, and the iPhone login still works. :)