Apple’s App Store is facing some new competition, and not just from the numerous app stores springing up from its handset competitors Nokia (NYSE: NOK), RIM (NSDQ: RIMM) and Palm (NSDQ: PALM). A number of alternative stores are cropping up to sell unauthorized applications for the iPhone, which the WSJ.com reports could threaten Apple’s sales. On Friday, a developer who has already created some popular iPhone software is launching Cydia Store, while a store called Rock Your Phone is rolling out shortly. Another start-up is planning an adult-themed content store for the iPhone. All are eyeing up the runaway sales at the App Store; brokerage firm Piper Jaffray estimates it brought in $150 million in revenues last year, and sales are expected to mushroom to $800 million this year.

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