We have a cellular data network connectivity problem. In our app, we are using both a Wi-Fi ad-hoc network and a cellular data network connection. The ad-hoc network is used to connect to a small Wi-Fi device (internal IP-address 192.168.0.12). This works great.
Also, we occasionally connect to our back-end server on the internet through the cellular data network connection. This sometimes work, sometimes don't work. We are aware of the fact that iPhone prioritise to send internet data on Wi-Fi (if available), but this is a Wi-Fi ad-hoc device, and does not operate in Infrastructure (routing) mode. So the Wi-Fi connection is purely internal. In normal circumstances, this also works just fine, both connections (Wi-Fi-device, server on internet) are working.
But sometimes, the cellular data connection just drops. You can see this visually in the top area by noting that "3G" has disappeared, and the "Wi-Fi symbol" is shown instead. If that happens, no cellular data connection is allowed. Our app cannot connect to the server on the internet, you cannot use the web browser etc.
We can fix this problem, although only temporary, by resetting the "cellular data" (or "mobile data" - not sure of the english translation) within the Mobile network settings. After the reset, both network connections works simultaneously again for a while.
Has anyone else noticed this problem? Could it be a bug in iOS (we are using iOS 6.0.1)? Are there any work-arounds?