PIT (Prague Integrated Transport)
Tram / metro / bus tickets can be purchased at all metro stations using the ticket machines (coins only) and tobacconists. Your hotel may also be able to supply them. Tickets are valid for 30min, 90min, 24hrs or 72hrs. Tickets must be validated using the yellow machine at the entrance to the metro or on boarding the tram or bus.
It is possible to buy tickets using SMS but you must have premium rate enabled. Text the following to 902 06:
DPT24 for a 30 minute ticket costing 24CZK
DPT32 for a 90 minute ticket costing 32CZK
DPT110 for a 24 hour ticket costing 110CZK
DPT310 for a 72 hour ticket costing 310CZK
If you are traveling with luggage, it too should have a ticket costing 16CZK (although we have yet to hear of anyone actually buying a ticket for their case - even though there's a 200CZK fine for not having one!)
The metro system doesn't have barriers but inspectors do frequently check tourists as well as locals. The fine for not having a ticket or traveling on an expired one is 950CZK - reduced to 700CZK - if paid on the spot.
The metro starts at 05:00 and runs every 2-4 minutes in peak time and 7-10 minutes off peak. The last metro leaves the end station at midnight on Mon, Tue, Wed, Thur and Sun and at 1am on Fri and Sat nights (or Sat and Sun morning if you prefer!).
More information on the Prague transport system can be found here