Update: The iPhone 3GS from Mobily is unlocked too. You can use STC’s SIM cards.
I have been receiving e-mails stating that Mobily employees are claiming that the iPhone 3G is locked to the Mobily SIM cards. Other employees claim that the next iPhone 3G shipments will be SIM locked. We and others tested the iPhone 3G and we confirmed that it is not locked to Mobily SIM cards. Apparently that was not enough. A friend that went to Mobily in Jeddah yesterday say that Mobily employees still insist that the iPhone 3G is locked to their network.
Feel free to print that table and present it to the Mobily employee who claimed that the iPhone 3G is locked to their network.
Thanks Rami for the link to the Apple support page.