The best way to arrive in the centre of Trevi is to take the bus from Foligno.  Check the timetable carefully, because there are not many buses, but the trip takes only 25 minutes and drops you conveniently in Piazza Garibaldi (where the walk begins).  An alternative is to take one of the frequent trains to Trevi from Foligno or Spoleto.  Unfortunately, the station is in the plain below the city: you can see the city from the station but  it is a long and steep walk up.  There are occasional buses to the centre - again, check the timetable.  In either case, buses only run on week days. 

Taxis are difficult to find.  On my first visit to the city, I arrived at the station and tried unsuccessfully to arrange a taxi from the local bar.  I ended up thumbing a lift.  I have since found two numbers for taxis:

1. ✴The Pro Trevi website (see below) lists 328 611 8880.
   

2. ✴On my last visit, my hotel arranged for a taxi from Dario Ciarelli, 328 953 3963.
   

My last trip in 2008 was for the Processione dell' Illuminata on the feast of St Emilianus, the city's patron.  I stayed at the excellent Hotel Trevi, but it has sadly closed: I am told that the Hotel alla Rocca is excellent.   I had a nice meal in the Osteria La Vecchia Posta in the main square (Piazza Mazzini).  Caffé Roma opposite is a friendly place to relax. 

The helpful Tourist Office is also in Piazza Mazzini.  Great resources for learning more about Trevi are the websites of the Commune and of  Pro Trevi.