Comcast is adding a social media element to its services through the acquisition of Plaxo, a contract the two companies announced Wednesday afternoon. Terms of the contract were not disclosed, but the purchase price is consideration to be in the $150 to $170 million range.

Joining forces with Comcast is a real win for Plaxo, with 1.5 million active monthly users. It’s a smart move by Comcast to bring the social media experience to its mainstream consumers (more than 30 million). Together, they will be able to help users connect with all the people they care about, across all of the devices they use, with all the media they love to consume, create, and share.

Big doings at Plaxo today! We are really excited to announce some of the biggest news in the history of Plaxo: We have just signed an agreement to be acquired by Comcast, the nation’s leading provider of entertainment, information and communications products and services (and our largest customer and partner) - said by John McCrea, VP of Marketing of Plaxo.

Plaxo will remain an independent operation in Silicon Valley, reporting into Comcast Interactive Media, which is a division of Comcast that develops and operates Internet businesses focused on entertainment, information and communication. Plaxo is developing an exciting roadmap with Comcast that includes socially enabling the media experience in places such as Comcast’s high traffic portal (Comcast.net),CIM’s popular interactive entertainment properties (such as Fancast and Fandango), and the television.

“Many users on Pulse share Flickr photos with their friends and family. We want to extend that sharing whether they are in front of the TV, on the phone or at the computer,” said Ben Golub, CEO of Plaxo. “Whether you are on Fandango (Comcast’s movie ticket service) or on demand TV, it gets that much better with social graph layered on top.”

Plaxo and Comcast have been working together for the past year on a number of initiatives. Plaxo is providing the universal address book for Comcast’s SmartZone communications center (slated to launch later this year), and they are also now hosting all of the address book accounts for Comcast webmail users. The partnership has already more than doubled the reach of the Plaxo network, bringing the total number of accounts to nearly 50 million.

“The address book and Pulse combined will change the way people navigate through thousands of choices of content,” said Sam Schwartz, executive vice president of Comcast Interactive Media. “You could know what shows your friends are watching, what they are downloading or what they are recording on DVR. Plaxo can help us build that vision. It’s less about the Comcast.net portal and more about bringing the social aspects to all media consumption.”

So, what about current Plaxo members? The services you know and enjoy from Plaxo will not only continue, but will continue to evolve and improve. In addition, both of their services benefit from “network effect,” which is to say that the more people who use them, the more useful they become.