In fact SIP has supported dial in/out for years -- you can get termination for SIP compliant phones from Vonage, using Free World Dialup, or from smaller termination only providers (similar to Skype Out/In) like EXGN -- there are literally hundreds of them. ALL the commercial gateways sold by Cisco and the other major players are SIP to PSTN (regular telephone system) gateway (or Cisco proprietary Call manager -- but not Skype). Even Skype themselves in the backend is almost certainly using SIP to get to the public phone network for their Skype In/Out system, since none of the major gateway companies build anything else, and Skype isn't building one off hardware, it simply wouldn't be economically practical.

There is also signifcant work to make SIP P2P to eliminate the central servers http://www.p2psip.org/ from SIP going on right now. As an aside, Skype isn't really even that P2P -- it uses central auth servers, so it is more of a hybrid system -- ala Napster -- in reality.

And with a SIP phone you can use *any* of those SIP providers. With Skype, you have one choice.

Skype is very good at making things work out of the box, hence the popularity, but there really isn't much (if anything) it can do that SIP can't. It isn't even that the P2P mattered. Skype's success is a matter of a very nice UI and user experience. They gained market on ease of use and marketing -- not bad things mind you -- not better technology. Kudos to Skype for making it easy for users to use VoIP, which was (and still is) notoriously hard to use with other providers. But the technology is different to allow Skype to lock up users, not to make things better from a technical standpoint.

Wow - some asshole thinks *that*'s offtopic?

Fine, let me put it another way, so that an idiot without rudimentary reading skills can understand.

High schools are not interested in you excelling at math. All their money has to go to making sure everyone can achieve the same level.

So it's up to you to pursue higher math education. I completed up to calc 4 in high school, but I was lucky that there were other interested students and administration support. I'm not sure I would have done it if the school (more than 10 years ago) hadn't made it easy to pursue.

But if you're a high school student who has to pursue it on your own (ie by taking a night class at a junior college), it's worth it!