I have no idea why people use their phone on the train for voice calls. The signal is just too flaky.
Consider this conversation:
"Hi there...I'm on the train...yes, yes I just wanted to let you know in case we get cut off...you know how people do...hello? Hello?"
"Yes, I know, terrible isn't it...you can never have a full conversation, can you? Uh huh, the signal is a bit dodgy...pardon? Hello? Hello?"
It went on like that for about 10 minutes, and absolutely no information was transferred apart from how bad phones are when used at 120mph inside a big metal can.
The worst one of these calls (and the reason why I no longer use my phone for voice calls on the train) was when my boss called me for a chat and we both were on the train at the same time. I don't think we managed any more than 5-10 seconds of connection. In the end I just turned my phone off so the call making/breaking couldn't continue.
Relax and watch the world go by, work, read, whatever...but just don't try and call anyone. Use texts or e-mail to communicate and enjoy that your messages will be received gratefully by the other end knowing that they didn't have to try and maintain polite conversation about how phones don't work very well on trains.