Here's the translated Czech text from the DPP web site:
The SMS ticket only applies in the P band. It does not apply to PID and suburban bus lines (lines 301-499 and 601-620). It does not apply in the tariff zones 0, B and in the outer bands (1, 2, 3, 4, 5, 6 and 7).
To use this service, you must have Premium SMS enabled. An SMS ticket can only be obtained with the Czech operator's SIM card. The prices are inclusive of VAT.
Passengers using an SMS ticket are obliged to board the vehicle (vessels) or to enter the metro or cableway to Petřín only with a valid SMS ticket on their mobile phone already accepted!
Passengers who are interested in issuing a tax document for an SMS ticket can check the document in the section Printing Tax Documents . Within the Portal, only HASH codes are retrievable from any SMS ticket purchased with no delay of 3 months.