Both of the main Omani carriers (Omanitel and Nawras) provide 3G services via their prepaid/pay as you go SIMs.
The best option is Omanitel. 1 Omani Rial for 24hours. This is enabled by sending a service text from a handset and then place the SIM in your iPad. A pain, but it works. You will need identification (passport is the most obvious) when you buy the SIM. The SIM will cost you 4OR.
*141*24# This gets you 24hrs for 1 OR.
*141*72# This gets you 72hrs for 3 OR.
Sending *141*[24 or 72]*0# will tell you when your current time runs out.
Unlimited data, but the speed is apparently capped at 64kbps.
Hope this helps someone
You can pick up a cheap nokia handset for about 9OR if you don't have a phone which will accept the Omani SIM, and it is a full phone sim, so it will give you an Omani phone number if you want to have people calling you in country or family from home using international calling cards.