Sep 15, 2010 15:16 GMT  ·  By

Spotify is about to mark a big milestone for the online music startup, 10 million users. According to the Music Ally blog, the company sent out invitations to an event to celebrate the occasion.

The figure has not been officially confirmed or announced and Spotify may not have passed the particular milestone yet. Still, in that case, it is very close to doing so.

There is one crucial piece of information missing from the invitation, whether the 10 million are registered users or monthly active users. For web services, this makes a world of difference.

But even more important for Spotify though is the number of people actually paying for the service. Spotify operates on a freemium model where the basic service is offered for free.

Users in the country where the service is available, just seven so far, UK, Sweden, Norway, Finland, France, the Netherlands and Spain, can install the Spotify desktop app and listen to any of the 10 million or so tracks available.

However, they'll have to put up with ads and make due without mobile applications. If they become paying subscribers thought, they can get rid of the advertising and have access to more features.

The most recent official figure about paying customers is from July when Spotify said it had 500,000 paying users. That was up from 350,000 in March.

By now, if the trend continued, Spotify should have at least 550,000 or maybe even 600,000 paying users. Still, that's just about 6 percent of the entire Spotify user base that actually pays for the service.

The issue of paying users has been a sore one for Spotify. The labels have been hammering about getting more people to pay and won't allow Spotify to launch a free service in the US. This issue has delayed Spotify's US launch for at least a year now.