All of us have probably tried to use Skype or other software that provide voice and/or video communication through the internet. The only requirement that both users should fulfill, is to have the application installed, and in some cases a registered account. When that is done, we can easily communicate without paying any fees. That sounds great!
Since the smartphone market has grown, more users can now afford a really good phone that allows them to use these software in the same way as on a regular computer. The only cost that might be a problem is probably the internet connection, but by having the right telephone contract, that problem would disappear.
That seems to be good for consumers, because you can call for no cost, but for the company that is providing telephony – no! If the income of the companies was before on the phone calls mainly, from now on, this ip-telephony might change the market dramatically.
However, some companies might block this port to prevent users from using this technique. So, before you consider to sign a new telephone contract, see if that company allows you to use ip-telephony, and if the port that, for instance, Skype is using is open.