By all reports, one of the most useful panels so far at this year’s South by Southwest Interactive (SXSW) conference in Austin, Texas, was Saturday’s iPhone: The New Gaming Platform, where some of the device’s most successful game developers shared secrets of their success.

The star of the panel, judging by the detailed notes filed by TUAW’s Victor Agreda, Jr., was Austin’s own Brian Greenstone, whose Pangea Software has racked up an impressive series of iPhone hits, including Enigmo, Cro-Mag Rally, Bugdom 2, Nanosaur 2 and Otto Matic.

Enigmo alone scored 810,000 downloads between July 2008 and January 2009 and cleared $1.5 million in profit.

No wonder Greenstone — who started out writing shareware games for the Apple (AAPL) IIGS and made his first fortune writing Mac games like the original Nanosaur, Bugdom and Cro-Mag Rally — has abandoned the Macintosh platform altogether and is now developing only for the iPhone.

For those who aren’t in Austin to see the panels or experience first-hand AT&T’s 3G overload problems, The Guardian’s Aleks Krotoski has kindly post