I was on tour recently and I am not sure if you are aware of this peculiar problem that train stations have with mobile phones.
If you switch off a old Nokia phone in a train station, you have to turn it on in that train station otherwise the mobile will not work. You have to take it to repair where they have to reflash the firmware to get it working again.
This is a big problem with the old phones, the brick like Nokia phones that you can find still being sold for 900 Rs etc.
So I was curious to see how the iphone would work. Most of the train journey I was switching the iphone into airplane mode to save battery.
But when I switched back on it just kept on searching for the network and couldn't detect. I was a bit scared and then realized this is a computer and what fixes most problems on a computer, restart and I did a restart and my phone was working normally again.
So if you switch off an iphone in a train station and turn it on somewhere else and don't get a network, just restart your iphone and it will detect the network.
I was using airtel sim by the way. i got the datacard sim with unlimited data usage which cost 1200 Rs per month so i could use Internet even when i was roaming.