Osnews.com features a review of Skype, the easy to use internet calling application. The review is mostly positive, however, it is also recognized that Skype uses no standard protocol (like SIP) and is therefore not interoperatable with other internet phone services.
I personally do not really like Skype. The internet only works because common standards are used. If the Skype protocol is that superior to other standards, why doesn’t Skype then release its specifications? Then Skype could be easiliy integrated into existing protocols and VOIP services.
In addition, one of the main promotion reasons for Skype is that its programme works with every network connection and every kind of firewall. But not only Skype can deal with a firewall. Also SIP compatible programmes like X-Lite today have no problems with firewalls and shared IPs. Using a STUN server, they can also connect to a telephony service when runing behind in a NAT. Furthermore, you can also use such a service with a dial-up connection. It is up to you which codec and therefore bandwidth requirement you choose. (It is even possible to use the Speex codec, which can be used from 2 kbps onwards.)
The other point is encryption. It is also possible to encrypt a call between SIP phones. Here I admit that this is until now still a bit difficult to set up for the end-user. Note also that the Skype Out function, which allows you to call regular phones, does not encrypt your calls.
The other thing is that Skype lacks a lot of features a SIP phone or the SIP provider offers. You don’t get a voice mailbox and you cannot be called from the normal phone network. Most SIP providers offer you phone numbers from the public telephone network and then everybody can call you even without a computer. When using Skype, the computer always has to be running. A SIP phone can just be plugged into your switch and it is operational.
I hope that the appearance of Skype promotes the other providers to make their products more user friendly. This is one of the main reasons why many people are not yet considering using the internet as a real substitute for their normal telephone.