How well a phone works depends on network coverage, radio performance of the phone, and its internal software stack. The radio performance of phones (receiver sensitivity, effective radiated power etc) depends to a large extent on its physical design, size of its internal antennas and so on. Radio performance is a constant struggle between what the phone designed wants it to look like, ever increasing complexity and number of bands etc, and there are a lot of phones around that are frankly pretty ropy just considered as radios so they may not work as well as they ought to given the available network coverage.
There are only a small number of manufacturers of the actual chipsets used in phones – about 3 now – and working on a network depends on a complicated software stack in the phone which come from the same suppliers. Because phones have evolved over 3 generations of digital mobile technology – and now a 4th coming in – and every phone has to work on at least 3 network technologies today (2G/3G/4G) there seem to be odd behaviours in chipsets from particular suppliers that persist in phones for years.
We have had at least 2 phones in the past that have exhibited an odd behaviour where, despite apparently having a good signal and showing they have service, they will neither make nor receive calls or texts. Once they get in this mode the only thing to do is to restart the phone whereupon you may get deluged with texts and voicemail alerts, and all the texts you though you had sent but were queued in the phone get sent. This seems to be characteristic of a particular software stack from one of the major chip vendors. We haven't seen it on recent phones (2 Motorolas) but my wife just got a new Samsung phone where we have had the old problem reoccur. Since the chipset supplier concerned dominates the industry it is quite probable that this could have caused your problem.
So there is a basis for what you are told though it's very garbled – if the phone and stack are working properly it should work seamlessly without restarting provided its home network or one where your home provider has a roaming agreement in place has coverage.