There are some more riscs in the VOIP world
The VOIP technology is using a lot of weak situations. Its nearly the same as with the youngsters / gamers.
So you cannot make any long term decision. VOIP market changes month for month and technology changes fastly. Knowing that, you should not invest in a time frame longer than 6 months. Currently SIP is becomming strong. H323 was strong in the past. Your hardware must run both.
Many (more than 5) vendors or VSPs are praying, their system is "the" only standard. Thats not true. They are almost lieing. Even not skype nor sipgate are the standard, they use a lot of "special" technology, which is not public.
The UDP protocol
They all are using the UDP protocol, totally ignoring that UPD was born for fast administration like "Ping" and "Traceroute". It was not built for data transfer. So if the volume of data passed using the UDP protocol will increase a lot, many large worldwide carriers will degrade the priority for this type of IP packets in their large scale core routers.
Many ISPs and carriers do not (or cannot) count UDP traffic, it was marginally extreemly low compared by TCP/IP traffic. At the end, it is a question of time, when the carriers will react and slow down th VOIP streams.
The result will (or may) be, VOIP is dead. It will be delayed to much, so the VSPs must buy expensive bandwith exclusively or they must rent their own dark fiber lines.
But they cannot get this for free.
Market penetration
One very riscful aspect is the market future penetration. Every new member or VOIP customer will no more dial out of the VOIP network. And all calls inside the VOIP islands are free (current situation in 2005).
So VOIP is softly killing its own profit base. Most of the VOIP providers are making their profits with outgoing calls in national or international PSTN network, undercutting the local telcos.
So VSP competition will be (or currently already is) desastrously growing, up to the time, no one has any profit to survive.
The business model is extreemly importatnt, to have a solid basis to survive the competition.
Inoperational codecs or sessions
Many VSPs try to set the standard. If you ask for bridges or gateways to other VOIP environments, the answer: "Take my offer, I am the only one."
But that´s not true. To many smallest and small and large companies did step into that market, driven by huge pain to find any field for profitable business action. Many VOIP vendors are declarig a beta status, others say, we are ready.
But that´s not true too.
Weak partnerships with hurry up cooperation
Many companies (with impressive names) have not the knowledge, to manage their own VOIP network, but doing the billing only and trusting the promisses of their partners. This results in a crowded operation and seriously corrupted invoices or wasted or missed prepaid budgets.
The consumed or stored minutes (or seconds) are passed from server to server, no more controlling is possible and the enduser has absolutely no control, what has been done with his prepaid credit. It is really time consuming for an enduser, to make sample survays, to check the billing.