Hi Kerry see this thread
http://www.totallyproperty.com/egyptian-lounge/6454-egyptian-sim-cards.html you can buy the simcards from Mobinil and Egypt Vodaphone - there is a shop in Naama bay but will be cheaper in Hadaba and Old Market.
To call another country from Egypt dial your country code then area code then the number. To call Egypt from abroad the dialling code is 002.
Local dialling codes are
Sharm 069, Hurghada 065, Luxor 095, Cairo 02, Alex 03, Aswan 097.
The cheapest time to call using a landline is after 8pm. If you want to make an International call then you can buy a Mena Tel card for around 20le and it will give you around 3 mins worth of calls anywhere around the world. The hotel room phones are very expensive so avoid
I think the sim cards are valid for 30 days and can be topped up.
Hope this helps
Alison