I just returned from Prague. I came across the Call Shop Inc which is situated by Narodni Trida metro station. The service provided by the Call Shop Inc is second to none, they really nailed the atmosphere etc.
They provide:
Cheap international calls from well designed telephone booths -even silk cushions! The call booths can get a bit warm, but the service and price make up for that minor problem. I paid approx 4.60 $US to call home for around 30 mins, the bill was itemised etc. Before that I was using the hotel phone to call home, what I paid at The Call Shop Inc was a fraction of the price. While I was there they had some students using internet and drinking coffee etc. Generally it was a nice atmosphere.
Overall I would say the service provided by The Call Shop Inc can be useful for many tourists, travellers etc. They do what they say and its the way that they do it that makes it exceptional.
From what I understand its run by a 2 foreigners who have been living in Prague for a number of years, they were very forthcoming with unbiasd tips and help when asked.