I've been reading a few things that suggest that the PSTN (Public Switched Telephone Network--the traditional phone system) is dying, soon to be devastated by VOIP. Since companies like Vonage are starting to switch consumers and small businesses, and larger companies have been moving internal phone service to VOIP for a while, within a few years most profitable customers will have have left traditional telcos for nice, cheap facility-less VOIP. That'll leave expensive customers (rural consumers, for example) as the primary users of the old phone system, and that'll destroy the business model of all of the telcos.
We'll see. Maybe it'll go that way, maybe it won't, but I wouldn't buy telco stock right now :-).
The story goes like this: once we have a good, semi-open way to map traditional phone numbers onto VoIP providers, we'll start seeing pure-VoIP calls between (say) Vonage and 8x8 customers. Companies can jump in and do direct VoIP calls to other companies and consumers using the same database, either the ENUM thing that never seems to go anywhere, something DNS driven, or something new. Doesn't really matter which way it happens, because one of them is going to happen very soon, probably within 6 months, and it's probably going to be at least partially driven by the Vonages of the world in an attempt to cut their costs when talking to customers of the other VoIP providers.
Once we have open-ish IP telephony, unless regulation rears its ugly head, phone service will end up looking a lot like email. Consumers and very small businesses will pay a provider, and larger companies (and geeks) will handle it themselves, directly. In either case, you'll end up paying someone to connect your calls to (and from) the legacy PSTN, so Aunt Mildred in Kansas can call you, but 95% of the traffic will be SIP end-to-end. Once this is in place, we can start exploring what you can really do with SIP above and beyond traditional telephone service (your phone number follows your laptop on vacation, for instance).
But, here's the problem: SIP spam. What's going to keep the spamming scum of the earth (and I'm being charitable here) from blasting your phone with automated crap 24x7? Regulation probably won't do it--they'll just connect directly (via IP) from outside of the US, just like some SMTP spammers do today. The economics are basically the same as they are for SMTP spam, it's astoundingly cheap to send, and you only need a few returns per million to break even. It's not completely clear that today's spam filtering techniques really apply to SIP spam, besides blacklisting and whitelisting.
I've been enjoying the near-complete lack of phone spam at home since the FTC do-not-call list took effect. I wonder how long the quiet is going to last, though.