The main difference between freespeech and Skype is that Skype uses a non-standard method for it's communications, freespeech uses SIP which is the worlds most popular standard for VOIP (Voice Over IP).
There some advantages and disadvantages when comparing Skype to freespeech.
1. Skype uses aggressive methods for traversing firewalls and NAT's (This makes skype work in more situations but is less predictable for an IT administrator)
2. Skype users can only call other Skype users for free - Freespeech users can call any other SIP provider for free (if the other provider permits it).
3. If you buy hardware with freespeech it can be re-used with any other broadband phone company using SIP.
4. Freespeech has more competitive call rates when dialling out to PSTN.
5. Freespeech is more localised and hence more suitable as a home phone replacement/supplement, for example local caller-id is presented.
6. The voice quality with freespeech is typically better (this is dependant on codec and conditions).
7. Skype will often re-use your local bandwidth for 'others' calls even when you're not using it, freespeech will not.