If you enjoy watching full-length Hollywood flicks on the small screen (and I mean very small screen), yet hate the time it takes to download them to iTunes and sync them, mSpot may soon become your favorite app.

Renting movies at the local supermarket may cost you next to nothing nowadays, and you get full TV-sized screen viewing privileges. But say you want to watch last years Oscar-winner while getting your cardio done at the gym. There’s now an app for that.

The mobile entertainment startup just launched its Mobile Movies site, which allows users to stream full-length movies on their iPhone, Android, Blackberry or Windows Mobile devices.

Facing stiff competition from Apple (which lets users sync their iTunes movie downloads to their mobile devices), it’s unclear if iPhone users will care for the convenience of streaming versus syncing. mSpot is betting that letting users start streaming their movies in real time (no downloading required) will help differentiate itself from Apple and other offerings.

Rumors that Netflix and Hulu are planning to launch mobile movie apps may also make it hard for mSpot to gain traction, which is why it’s extremely important that they get themselves known – and downloaded – as fast as their videos supposedly start streaming. They already have already taken the leap from working on Sprint-only devices to now being carrier agnostic (well, they at least work on the four major carriers in the US.)

For $4.99 each, you can rent an individual movie, or app users can subscribe for a monthly membership allowing four movie downloads at a rate of $9.99 per month (higher-priced subscriptions for more movies are also available.)

I wonder if that price could be reduced by selling mobile ad space, especially upcoming film previews at the start of ones mobile film viewing. The user paying $4.99 to download one film to their phone is someone with money to spend on media, and there’s a lot of potential marketing that could be done in exchange for free downloads — ie, sponsor a free film download and promote your media-related company in the least obtrusive way possible in your sm screen all movie.

mSpot has scored deals with Paramount, Universal and The Weinstein Company to stream the flicks on mobile devices. At launch, they have 350 movies available to stream. mSpot is a mobile entertainment company that delivers music, movies, radio and TV to more than six million mobile customers across 10 wireless carriers.