I use this Gizmo and other internet phone software services (like Skype) before. Heres my 2 cents :
- this type of services is good for people who wants to make international calls to fixed line or mobile though the software also provide PC to PC (free) connections like MSN
- the attractive part is cost. Gizmo provides free calls (subjected to 10 mins per day). This is good for people who just want to call their family members and say hi, greetings and/how are you each day. If you need longer talk time, you can sign up for their call out services, its relatively cheap as well. Skype provide same services except the per min cost is higher.
- Line quality wise, Gizmo can sometimes mess up the calls. I have a few occassions where the line was routed to another person mobile. And during peak hours (like evening time in Singapore), calls connection can take quite long or even unsuccessfully. Skype on the other hand never fails me . Sound quality wise, Gizmo is average and Skype is pretty good.
Thats all my experience