Free calling and texting apps face a triple threat to long-term viability

The list of apps that offer free texting and voice services on iOS (s aapl) devices grows longer every day. Viber is one, as is Vumber, which now provides cross-platform Android (s goog) and iOS calling. These apps have a noble goal: provide users with an alternative to managing costly voice and text plans from carriers in addition to the data plans they must have in order to take advantage of everything smartphones have to offer. But they also come with a big downside: These apps are only as strong as their network of users, (since in most cases, free calling only happens between users who have the same app installed on their device), and as the data network that allows them to exist.

Apps like Vumber, Viber, WhatsApp Messenger and even, to some extent, Skype (s msft) depend on users getting others to sign up to take advantage of the cheap or free rates. Research In Motion’s BBM (s rimm) works on roughly the same concept, as does the recently announced iMessage, although since both are pre-installed on specific hardware, their reach will be much greater initially than third-party offerings.

While I applaud any efforts to provide competitive alternatives to overpriced carrier talk and text plans, I think the network flaw for this kind of startup will eventually turn out to be a fatal one. For example, Google already offers a much more flexible option via its Google Voice service, and one that’s compatible with landlines and traditional cell phones out of the box. If Google Voice ever does expand worldwide, it’ll take a big dent out of potential demand for smaller VoIP offerings.

And while Google Voice is a looming threat because it doesn’t just work with itself, there’s another potential industry-breaker that already has the network part down, and just needs to expand its communications platform. I’m talking about Facebook, which, if it gained cross-platform voice support, would quite quickly rise to the top of the VoIP field.

Finally, carriers aren’t likely to take the circumvention of their services lying down. Already, we’ve seen capped bandwidth plans pretty much take over mobile broadband, and some carriers have even prohibited the use of VoIP services over their data networks.With Google and Facebook stalking the seas of free mobile communications, and carriers doing what they can to either discourage the practice or  I’m not sure I’d be too eager to swim with anyone else.