Hi SConway -
Telephone coverage in Switzerland is excellent, with the only exceptions being in in the most obscure regions of the high mountains:
scmplc.begasoft.ch/plc app/pages/gis/netzabde ckung.jsf?lang=en
Wifi is almost but not quite universal in lodgings, and will be excellent in the major tourist areas. Roughly 99% coverage of Switzerland's populated areas. I use Google Maps on my smartphone regularly.
For travel by public transport in Switzerland, this map, with "Traffic" turned on in the menus, permits you to get the exact station/stop name for every stop in Switzerland. Useful when putting names into the timetable:
map.search.ch/?pos=641788,160504&z=32 &poi=bergbahn,halteste lle,zug
Mouse over the icon for a station.
You'll note that the rail lines show up very clearly once you zoom in far enough.
A few of the simpler rural inns that I stay at don't have good Wi-Fi.
As a consequence, I rent a portable WiFi hotspot and have fast service everywhere the phone networks reach. This link has good information on that device:
1960man's reply is correct, although bookstores are rarer than they used to be. Convenience stores in addition to "Kiosk" are common, at stations and in many villages and towns, and often have maps of Switzerland in addition to local hiking maps. They include "Aperto" and "Volg." Local hiking maps tend to be available everywhere in Switzerland.
The hiking link in My SwissAlps is focused on hiking maps:
If you have time, and are coming from the USA, you can find Michelin maps of Switzerland frequently in Barnes and Noble bookstores, and certainly on Amazon. Since I do not know your travel times or exact destination-
I cannot be more precise.
However, each of the towns and villages in the Jungfrau region will have a store where you can buy maps....more focused on local maps, but they should have an "all- Switzerland" map. Sporting goods stores often have maps , at least for hikers.
Trains from Zürich Airport to the Berner Oberland all pass thhrough Bern. Some do not require change in Zürich main station. Others do. If you stop in Zurich main station , Barth Bücherei, one level down near the steps to track 2 has a wide range of maps of all kinds, as well as travel books.
www.sbb.ch/content/int ernet/sbb/en/bahnhof-services/bahnhoefe/bah nhof-finden/bahnhof.3016.ht ml
Zurich airport has "Press and Book " stores airside and in the train station travel center:
www.sbb.ch/content/int ernet/sbb/en/bahnhof-services/bahnhoefe/sho pville-zuerich-hb/geschaefte/shop-detail.html/geo-alfred-barth-ag-69dd
A Google search for Bookstore in Interlaken reveals a few bookstores.