Here's a strange story for you: Apple has worked with China Mobile to resolve issues with the iPhone 4S on the Chinese carrier's network. What's strange about that? China Mobile doesn't officially carry the iPhone 4S...
Electronista is reporting that some 4S users cannot activate SIM cards or make calls with a full signal. The issues appear to be due to the iPhone 4S only supporting the GSM P band (885 - 915 MHz) and not the E band (880 - 890 MHz), both of which are in use by China Mobile. The P band is primarily used for outdoor use, while E is designed for indoor areas -- train stations, conventions centers, and the like. When China Mobile users move into an area without P coverage, they still see full signal strength, but the connection is dropped.
According to China Mobile, Apple has updated all iPhone 4S devices built after February 8th, 2012 to work properly with their network. China Mobile is also saying that Apple is planning to issue a firmware update for earlier 4S devices in the next few weeks.
Penn-Olson reported that there are some 15 million unofficial iPhone users on the China Mobile network at this point -- people who love their carrier so much that they're willing to run the iPhones on a system that doesn't give them 3G service. China Mobile expects to become China's third iPhone carrier soon, and is hoping to build a 4G LTE network that may be useful with the next generation of iPhone.