SEATTLE – After a series of leaked prototypes, it’s almost a given that Apple Inc. will unveil a new version of the iPhone during its annual software developers conference that opens Monday in San Francisco.

The revelation of a splashy new iPhone would clear up one of the highest-profile Apple mysteries of the year — second to the existence, confirmed in January, of the iPad. Yet it would leave another unknown simmering at Apple, one with far-reaching implications for how we listen to music.

First, let’s talk iPhone.

Apple won’t comment on its plans, but it has used this conference to launch the past two generations of its smart phone. In April, Gizmodo, a tech blog, paid $5,000 to obtain a working iPhone prototype that was lost by an Apple engineer in a Silicon Valley bar.

Apple didn’t say the prototype represented the next model of the iPhone, but if the descriptions posted online are accurate, the device will be getting a clearer display, longer battery life and a front-facing camera that could be used for videoconferencing. It’s also likely to have the updated iPhone software Apple previewed in April that makes it easier for users to run more than one program at a time.

In another sign Apple is preparing a new model, Walmart Stores Inc. in late May halved the price of one kind of the iPhone 3GS, the model that debuted last year, to $97.

Apple is also likely working on a service that could change the way many of us think about buying and listening to music, though it may not make an appearance during CEO Steve Jobs’ presentation Monday.

As Apple’s iPhone and other smart phones became more popular, new services started sending music over the Internet straight to the devices, letting users skip the step of plugging in and transferring songs from a computer, as iTunes still requires. Such services, including Rhapsody, give people access to just about every song imaginable for a monthly fee.

Forrester Research analyst Sonal Gandhi said these streaming services are still too small to lure Apple into directly competing. But Apple does need to keep an eye on Google Inc., which is building music-streaming technology into its increasingly popular Android phones. Google acquired the company Simplify Media this year and said in May it plans to build a desktop program that can beam people’s iTunes libraries over the Internet to Android phones.

Apple may be cooking up something similar. In late 2009, Apple bought Lala.com, which gave customers a way to listen to songs online, anywhere, if they had already purchased and stored the tracks on their own computer.