(Updated with photos) Sprint today officially started sales of the Palm Pre, its first multi-touch phone and what’s been regarded as the most direct contender with the iPhone. Initial reports of stock sent to Electronista vary and show that both supply and demand vary heavily depending on the region: Sprint stores, particularly in major cities like New York, have relatively large supply of as much as 100 or more. However, third-party stores like Best Buy and Radio Shack have relatively much smaller supply and little to no queuing.

Leaks from within Best Buy ahead of the launch had suggested the retailer may not have healthy supply until July, prompting speculation either that Sprint’s stores were favored much more heavily than others or else that supply was so low that third-party stores couldn’t be guaranteed reliable stock. No slips have surfaced about Radio Shack’s availability ahead of today’s debut.

The Pre’s key selling point is webOS, which debuts on the phone. Besides offering a comparatively intuitive, finger-driven interface and full HTML web browsing, it offers a handful of key features that will be absent from its Apple rival even with iPhone OS 3.0, including true multitasking for features such as background Internet radio, universal search that includes Google, Twitter and Wikipedia, and an online sync concept known as Synergy that can merge contacts and calendars from the phone, Google and Facebook while automatically eliminating duplicates. Lighter restrictions on third-party apps allow PalmOS emulation.

A 3-megapixel camera and a slide-out hardware QWERTY keyboard are its key advantages over the current iPhone; otherwise, it has 3G, 8GB of built-in storage, GPS and Wi-Fi much like its key challenger at the $199 price point.

Both Palm and Sprint are depending heavily on a successful launch to turn around struggling businesses but have been helped by mostly positive reviews that praise the operating system while raising concerns about the keyboard and some minor but notable build quality concerns.