SIP Failed, now what?

I went through a couple of articles and now I can not recall exactly what made me believe that it is still possible with SIP to do all this.
Probably the following paragraph:


So your decision will be taken considering PSTN line costs. In fact what VoIP does is the convert this:

Home Telephone1 --- (PSTN) --- Home Telephone2
             PSTN great distance calling cost

into this:

Home Telephone1 --- (PSTN) --- PC1   +
      PC2 ---- (PSTN) --- Home Telephone2  =
      --------------------------------------
          2 PSTN short distance calling costs

To save money you need that:

2 PSTN short distance calling costs < PSTN great distance calling cost 

or this one:

A typical application is like that:

Home telephone1 -- (PSTN) -- PC1 -- (Internet) -- PC2 -- (PSTN) -- Home telephone2

Home Telephone1 make a calls to PC1 phone number (using PSTN line, I mean classic telephone line).
PC1 answer to it.
Home telephone1 must tell PC1 what gateway use (PC2 in this case) by giving the IP address (from DTMF keyboard) and/or what number call (in this case Home telephone2).
After that PC1 will start to make an H323 call to PC2, then it will pass Home telephone2 to PC2 to make it call it throught PSTN line.
Home telephone2 answers to call and communication between Home telephone1 and Home telephone2 begins.