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Google (GOOG) on Tuesday began sending out invitations to purchase its $1,500 Glass wearable device to users of its All Access music subscription service.

The invitations are Google's latest effort to expand its program of early users of Glass, its high-tech eyewear device. Glass is worn like a pair of glasses, and connects to users' smartphones to relay messages and make phone calls. The device is also capable of shooting photos and video as well as running smartphone-like apps that are called "Glassware."

Google sent out the first invitations for Glass in early 2013, and since then the company has slowly been expanding the number of users who can purchase the gadget.

The invitations to All Access users were sent to coincide with launch of Google Play Music on the $1,500 device. Google Play Music All Access is a service available for $9.99 per month that lets users stream music from the Internet on their devices.

"Interested in rocking out while exploring with Glass? Sign up to receive your invitation below!" Google said in an email, according to AndroidCentral.

Google is expected to release Glass to the general public sometime next year, and it may do so at a lower cost than the current $1,500 price tag.

For now, those eager to use the device can head to Ebay or Craigslist, where a number of users are selling Glass devices for several thousand dollars apiece. Others are selling invitations to purchase the device directly from the company.