In a previous question, I asked why should I use SIP when my application built on HTTP works fine. You replied that SIP provides URL dialing. Yet so does my application, with better session routing for all packets. Would you please elaborate?
Can you give me any idea how much it will cost me to setup a SIP environment in an office, with SIP proxy and registration? How much will a STUN/TURN server cost? How much does heavy client of SIP increase the price of a telephone set?
There are a number of options that can make different systems have a significant range in pricing. The same would be true for a STUN/TURN environment. Your best bet is to select a couple of vendors and compare them. There are some great ROI papers on SearchVoIP.com that can help. Beware that STUN will not work behind symmetrical NAT (Network Address Translation), also known as bidirectional.