Its purpose is to let your mobile or PSTN phone ring whenever somebody calls your VoIP number. It also makes use of Sipbroker's access numbers so that friends from wherever in the world can call you for the price of a local call.
Although you can tell from the comments to Vinay's blog post that his solution is a quite difficult to understand, it's definitely worth reading. I would like to add that Vinay's solution rocks even more when you extend it with more inbound numbers from Tpad and Gizmo Call.
Another elegant solution for the same purpose could be the GSM gateway from 4S newcom:
Redirection of fixed office numbers to mobile phones works by routing an incoming call to an employee's desk phone to the employee's mobile phone, using the appropriate GSM channel on the above-mentioned GSM module. The call will then be completed at no cost.The PBX from 4S newcom receives the phone call and forwards it to the cell phone over a built in GSM device which holds a SIM card with flat rate tariff, as you can read here.