Not to be outdone by Spotify, Pandora and MOG, Rdio has announced that it will launch a free music streaming option. Launched last year by the founders of Kazaa, Skype and Joost, Rdio charges $5 a month for songs on your computer or $10 a month for additional platforms such as your smartphone. Although it offers a one-week trial, the company hasn't dabbled in the freemium space yet, but it plans to take the plunge in the very near future.

Unlike its competitors, Rdio's free service will reportedly lack advertisements. Instead, it seems like free accounts will be hindered by a time restriction. For instance, Pandora caps free users at 40 hours per month and they have to pay to keep listening. Rdio hasn't elaborated on its plans yet, but it has clearly stated it's not trying dissuade users from subscribing. On the contrary, it believes free users will be compelled to sign up for the full service.

Rdio's announcement followed sharply after MOG shared its freebie strategy. Like Rdio, MOG charges $5 to stream tunes on your computer or $10 to access them with a smartphone. However, instead of prodding users to subscribe by capping their consumption, MOG plans to cash in on frugal users with interactive ads and promo tactics. These also serve as an annoyance that encourage people to subscribe, but they let MOG profit regardless.

Non-subscribers will see a virtual "gas tank" called FreePlay (it's already on MOG's main page) that shows how much free music you can listen to. As the tank runs dry, users will be able to replenish the free tracks by watching movie trailers, sharing links with their social networking contacts, creating and sharing playlists, listening to new artists and other such actions. In fact, it sounds like MOG plans to offer free music for random occurrences.

"Sometimes you might do things like add Bob Dylan to a playlist, and because we like Bob Dylan, we're just going to give you free music," said MOG founder and CEO David Hyman. "There will be serendipity, and you'll get free music for events that you wouldn't expect." It's debatable whether this is truly free, as you're still trading time and energy to access music. Nonetheless, it's a novel approach and we imagine many will appreciate the value.