The program (CSipSimple) seems to work not well when cell data network is unstable. It works OK hovewer if you manually switch it on and off.
How to simulate bad network connectivity (e.g. going by underground train) for testing the application?
It should be mobile network, not Wi-Fi.
Are there any programs or hacks (in software, with root access) for this or I should resort to wrapping the device in foil?