It doesn't exist yet, but you know it's coming. Spam on your cell phone is only a matter of time.

Once the province of small companies like Vonage and 8x8 (NASDAQ:EGHT), Voice over Internet Telephony, or VoIP, is now spreading to all the large telecoms. AT&T (NYSE:T) is making a last-gasp effort to survive by embracing Internet telephony; SBC Communications (NYSE:SBC) is equippingFord (NYSE:F) offices with the capability; and Verizon (NYSE:VZ) offers its own package. Alyce Lomax also notes that cable companies like Cablevision (NYSE:CVC) and Time Warner (NYSE:TWX) are offering their customers the service, once again invading the turf of the telecom giants.

Enterprise level VoIP is expected to grow 20% annually through 2009, according to Insight Research. Even though they are no less expensive than traditional PBX phone systems, VoIP systems offer the potential for greater worker productivity by combining voice and data services. For example, employees can access voice mail while working on their laptop.

Consumer adoption of VoIP is also expected to grow exponentially. Currently there are only about 131,000 residential subscribers, but it's estimated that by 2008 some 17.5 million subscribers -- one-third of all households in the country -- will have Internet telephony. Its growth is being fueled by the fact that it's cheap, avoiding (for now) the taxes imposed on landline calls, and that the connections are becoming faster.

And with this explosion of VoIP will come the attendant annoyances that accompanied the explosion of the Internet, namely spam, the unwanted junk mail that clutters up your inbox.

VoIP spam, also known as SPIT, for SPam over Internet Telephony, doesn't actually exist yet. But that hasn't prevented privately held Qovia from patenting technology to block it. Funded by Anthem Capital Management, Canaan Partners, and Nokia Venture Partners -- the venture capital arm of cell phone giant Nokia (NYSE:NOK) -- Qovia's technology uses algorithms that look for call characteristics that resemble spam and blocks them before the calls are directed to recipients. Some of those characteristics might be multiple calls from one location as well as multiple calls of the same duration.

However, I would refrain from telling your wife that her daily reminders to stop and pick up milk are equivalent to SPIT.

Companies would also be able to block calls from certain domains similar to the way email can be blocked, though content filters that identify certain words or phrases would be harder to implement because of variations in pronunciation.

Right now Qovia is a solution in search of a problem. There has not yet been the widespread adoption of the technology to make spamming, or spitting, profitable. Yet if the problems of spam are any indication -- salacious messages, stock scams, viruses, denial-of-service attacks -- the problem shouldn't be a long time coming.

Voice-mail spam, like the vice presidency, as Jack Nance Garner, the 32nd holder of the office once observed, is not worth "a warm bucket of spit."

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Fool contributor Rich Duprey actually enjoys some of the spam he gets but would frown on being spit upon. He does not own any of the stocks mentioned in this article.