Well regarding phone masts or satellites etc and, ignoring for a moment the need for a 'time machine' to exist prior to the time you want to travel to ie if this were an example of a time traveller, the time machine would have to have been built no later than 1928 so, are the travellers ET's, there are a couple of options
1, the people who solved the time travel conumdrum also solved the ability to communicate across time or
2, the communication device the 'traveller' was talking into wasnt a mobi but another device for communication or
3, the person the supposed time traveller was talking too wasnt that far away so negated the need for a relay mast of satellite.