Back when Steve Jobs announced the iPhone SDK, he told excited developers that the only applications Apple wouldn't be permitting through the AppStore were those illegal or pornographic.  Now that some of the dust has settled - and those 100,000+ coders sitting down in front of the SDK! - questions are being asked about just how accurate that statement was.  While it's open-season for mobile entertainment software such as games, productive apps or messenger clients, developers behind services such as Rhapsody or Napster, who would rival Apple's own iTunes store, are curious to know Steve Jobs stance on them creating programs for the iPhone.

"It's an open question at this point how amenable Apple will be to offering products or applications that could conceivably interfere with its own iTunes revenue stream.  The real interesting test case will be Amazon.  Here's a music vendor selling songs that are clearly compatible with the iPhone. Unlike with Rhapsody or Napster, there's no DRM you need to make work" Ross Rubin, analyst, NPD Group

Meanwhile, the possibilities for music streaming services such as Pandora or Last.fm are also unclear.  SeeqPod, which advertises itself as a "playable search" client, has been offering an iPhone-formatted version of their streaming music service since shortly after the handset first became available, but there is no word on whether they'll be allowed to develop a standalone app rather than rely on users navigating to them in Safari. 

Apple's own SDK guidelines seem purposefully to stand in the way of rival music software.  The well-popularised "no background processes" clause would render an iPhone (or iPod Touch) running non-iTunes music apps useless, since the playback would not be allowed to continue while other functionality was used.  In fact, the guidelines for third-party software would seem to suggest that no music app could satisfy Apple's demands for a seamless user experience:

"It's important to make sure that users do not experience any negative effects because of this reality. In other words, users should not feel that leaving your iPhone application and returning to it later is any more difficult than switching among applications on a computer" Apple SDK documentation

Since plugins for Safari or iTunes are similarly out of bounds, that limits functionality-increasing additions such as Last.fm's music suggestion widget.

Apple has so far limited developer sign-ups, ostensibly because of the sheer number of interested parties, but it would be interesting to hear how many of those accepted into the iPhone Developers Programme are considering coding potential rivals to the company's music download business.