Apple chose not to hassle Real Networks over the Rhapsody iPhone app, apparently. It's on iTunes today, perhaps because Apple expects limited uptake given the price of Real's service.

The app itself can be downloaded for free, but it only streams music from Rhapsody if you pay for Real's $15 a month "Rhapsody-To-Go" mobile service, which is a premium over the standard $13 Rhapsody service and only works with Windows PCs.

(To clarify - if you have the standard "ultimate" service, you can upgrade for $3 more a month to use the app.)

It's a cool application - it streams songs from Rhapsody's library of more than 8 million songs to iPhones and iPod Touches and can be used to create playlists or play Rhapsody radio stations - but iTunes apps generally have to be cheap to be hits. How many iPhone users will be interested in a $15 month music service on top of their already expensive service plan?

Investors seem to think a lot - Bloommberg noted that RNWK climbed as much as 14 percent today on news of the app approval. Wow.

At last check it was up about 7 percent, to $3.63, but maybe Wall Street is more impressed with the buzz around Rhapsody releasing the new Jay-Z album "The Blueprint 3" two weeks early.

The $15 cost isn't shown on iTunes, although the app's description mentions - in the third paragraph - that a subscription is required.

Real provides a seven-day free trial of the mobile service, which is stingy compared to the 30-day trial offered on the desktop service.

Real's announcement said the company will release an Android version later this year and is looking into versions for Windows Mobile, Palm Pre and other phone application outlets.