In what appears to be a sign of the times for Research In Motion (RIM), YouMail on Friday announced via its official blog that it is abandoning support for the BlackBerry platform. 

YouMail, which provides voicemail service, has just released a final version of its app for BlackBerry, but that will be it as the company discontinues support for the platform altogether. BlackBerry was the first smartphone platform where YouMail started doing app development. The company credits BlackBerry with securing its first 1 million users.

In a blog post, the company called the decision “bittersweet,” but added that over the past year it has seen its BlackBerry audience steadily shrink, “with a steady exodus of those users moving to the iPhone and to Android (where fortunately, they’re tending to keep YouMail as their voicemail service).”   

“And we’ve also seen the number of BlackBerry users/day plummet while Android and iPhone users have soared,” the blog noted., adding that “it’s sad, but on many days we’re now getting fewer BB users than Windows Phone 7 users, and we don’t even have a Windows Phone 7 app!”

The new free app release features a number of big fixes, as well as the elimination of ads. YouMail said in its blog post that there’s always a possibility of returning to the platform.

“If BlackBerry stages a comeback (we’re rooting for BB10 to take off!), or we can figure out how to drive a meaningful number of new BlackBerry users, we’ll be back,” the company said.

Lagging developer support has been one of the main criticisms leveled against RIM in its bid to produce a consumer-oriented high-end smartphone that can compete with the likes of Android and iOS.

RIM has been struggling with multiple delays to the launch of its QNX-based BlackBerry 10 platform, upon which the company plans to base all future smartphone models. In the first quarter of 2012, BlackBerry controlled 13.4 percent of total smartphone OS market, down 3.2 percent sequentially, according to comScore.