I'm sure I read a study about mobile phone usage in cars which showed that the distraction effect of using a mobile phone while driving, even just looking at the screen, continues a short while after you stop using it. I'd struggle to find it now so take that with a pinch of salt.
The important point here is that not everyone deals with distraction the same, though. For some people, they have a higher ability for multitasking and remaining safe than others - thus how some drivers can be all over the place just looking at a phone, whilst plenty others use them day in, day out, without incident.
I'm not here to challenge the laws etc, just to point out that just because a study says it creates a distraction, it does not follow that you are, therefore, unsafe.
Bringing it back to trains, there are a whole plethora of other cab based distractions that could be pointed to, that create a similar or higher level of distraction. The key takeaway is that managing your workload (which is a fundamental part of much driver training) is very much a part of your duty. Whatever the mobile phone policy, whatever the distraction, as a well paid professional its our jobs to keep things safe and exercise professional judgement - some policies at some operators really water down the level of professional judgement, at others it leaves a lot more room for it.
The problem with overly strict policies tends to boil down to the implications this has on the passengers. Take, for example, the above 10 minute policy. If a driver needs to phone maintenance control to resolve a fault, does he then have to sit stationary for 10 minutes before moving the train (thus adding 10 minutes to the already delayed service) before being able to check if the fault has been resolved?
I'd also bet good money that any other drivers out there on this forum can think of a good few times where a train fault or degraded working scenario has created a far greater distraction than a mobile phone ever could, and indeed, in such a scenario a more lenient policy around being able to switch a phone on might actually have helped in resolving the situation and reducing workload.
To be clear, I'm not at all suggesting anyone should be using a phone on the move. The GSMR is for that purpose. But at a stand is a different matter. Whilst some policies are well intentioned, they often prevent sensible and appropriate use of technology. Ultimately the end user is often the one most inconvenienced as a result.