Once upon a time, text messaging was an exclusive feature provided by a mobile device. And though instant messaging services and apps are often viewed as substitute produces, text messaging has remained largely a “mobile” feature. There are notable exceptions, however, offered by Pinger and Google (News - Alert) Voice.

also can be used from the Xfinity Connect Web site.

Text messaging also is available online via the Xfinity Connect web portal, which provides quick and easy access to email, voicemail, Twitter (News - Alert) and Facebook, as well as Contacts, Calendar and DVR management.

Text messages by Xfinity Voice can be sent for free anywhere in the country and to more than three dozen countries worldwide, including China, Brazil, Canada and eventually Mexico. More countries will be added in the future, Comcast (News - Alert) said.

For a fixed network service provider, text messaging features blurs the distinction between fixed and mobile service. In a general sense, that is an example of “fixed mobile convergence,” an instance of enterprise unified communications systems.

The Comcast move represents an extension to the consumer market, as Pinger (News - Alert) and Google Voice have done. Comcast’s move also illustrates another aspect of how competition between apps and services occurs.

Over-the-top communications apps typically gain favor with business and consumer users because they offer either “no incremental cost” or “much cheaper” use of features users have had to pay for in the past.

In this case, Comcast has slightly different expectations. The company does not expect people to stop using their mobile devices. But the new feature makes the fixed network communications service more valuable, and akin to mobile service in an important way.

What remains to be seen is the value users will perceive, and the extent of its use. The new feature could be valuable to some users on text messaging plans that have usage limits a user frequently approaches or exceeds.

For some, the visual voicemail feature will probably have more utility.

We are likely to see similar implementations in the future, especially as fixed network voice suppliers stay relevant in a market where mobile has become the preferred medium for “voice.”

The ability to use an existing Sprint phone number as a Google Voice number, with unified voice mail, is not a "full" implementation of unified communications. But it offers a feature that has always been the main attraction of unified communications and fixed-mobile convergence.