Prepaid lines are either 200 - 300 QR depending on the plan, and you usually get 50 - 100 QR worth of credit and either 60 - 360 days validity (extendable of course). During promotions the price is usually slashed to 100 - 150 QR.

Local calls cost 0.55 QR per minute at all times
Int'l cost IDD rate + 0.55 QR per minute

Local SMS: 0.40 QR
Int'l SMS: 0.60 QR
Local MMS: 0.90 QR - 1.20 QR
Int'l MMS: 1.35 QR - 1.80 QR
Mobile Internet: 10 QR for each 1 MB

Postpaid lines cost 250 QR connection fees (paid once) and roughly 65 QR per month for rental

Local Calls: 0.35 QR (peak rate) - 0.30 QR (off-peak rate)
Int'l Calls: IDD rate + local call rate per minute
Local SMS: 0.30 QR (peak rate) - 0.20 QR (off-peak rate)
Int'l SMS: 0.60 QR (fixed rate)
MMS & Mobile Internet rates: same as prepaid

hope that helps