Spotify made its long-awaited U.S. debut Thursday, promising users a streaming music service that will run well on operators' 3G networks.

The music application will be available to U.S. consumers as an invite-only (for now) free, ad-supported mobile and desktop app or as a US$4.99 paid subscription service for access to its millions of tracks.

Motorola Mobility LLC is partnering with the company at launch, giving its customers early access to a $9.99 Premium version of the on-demand service that lets users stream to Android-based smartphones. The Premium service will also run on iPhone, Symbian Ltd. , Windows Phone and Palm Inc. devices. (See Spotify Launches App for iPhone, Android.)

Here's Spotify tooting its own horn:

Why this matters
Spotify is the type of service that will show the true power of 4G Long Term Evolution (LTE) networks in terms of speed and latency, but it will also test the limits of operators' already-stressed 3G networks in the U.S. The company says it expects to perform just fine on 3G. Its FAQ recommends 256Kbit/s for optimal performance. (See Happy Birthday, LTE! )

The site says: "Spotify usually works well on a 3G connection. Plenty of free disk space also helps keep the network requirements down as it enables more caching."

The U.S. will be a critical market for the company for more than just performance, however. Spotify's rampant success with more than 10 million Europeans earned it a spot on Light Reading's list of companies to watch this year, and could give other music services such as Rhapsody Networks a run for its money. (See Leading Lights: Mobile Services/Apps Finalists.)

Getting to the States was no easy task, either. Negotiations with music labels have held the launch up for nearly two years, and the app's success will depend on its ability to scale, as well as to forge partnerships with wireless operators. Informa Telecoms & Media says Spotify could fare well if it can replicate what helped it win over Europe and feed off the strength of its free service. (See Virgin Media Teams With Spotify and 3 UK Teams With Spotify.)

"In a sense, it must simply repeat the formula that has served it so well in Europe: A clean, intuitive user interface, deep links with properties like Facebook and Last.fm (a Pandora deal is not out of the question) and high penetration across mobile handsets and other devices," Informa Principal Analyst Giles Cottle writes in a research note.

For more
Read up on streaming music and its effect on wireless networks:

— Sarah Reedy, Senior Reporter, Light Reading Mobile