If they can time travel and are able to use trans-temporal communications devices, why on earth would they need to hold anything, it could be jacked straight into the human body
For those of you suggesting that "technological devices" could be implanted directly into the body in order to communicate - although this technology will exist (and perhaps already does), how many people would like this done to them?
We live in 2010 and only "technological devices" which we have clamped into/onto our body are prosthetic limbs, hearing devices, pace-makers, metal plates etc. And these devices are very much as a last resort and relate to medical conditions.
Yes, in 2010 or 2110, they could very well have implants, but very few humans would be happy to them implanted into them.
Humans of 2010, in general, do not like the idea of implanting foreign objects into their bodies and do so only if it improves their physical appearance or is a medical requirement.
It is not beyond the realms of possibility that time-travelers (if they will ever exist), should bring communication devices with them. In fact, it seems almost a given that a time traveler will bring a communication device with them.
With regards to the lack of phone masts - in a century or 2, it may well be possible to use communication devices which do not require masts. It may be possible to link 2 communication devices, directly, with a built-in mast.