All of the following are ways to save money on transportation except:

A; Cell phone

B: A Private phone line

c: phone card

D: a VoIP service

The options listed are not related to the question. and if they were related in any sense then I would say the cheapest thing on the list is a phone card so I guess you can buy that and save the most for your travel as you can use phone cards anywhere as they have 1800 numbers which are free from any public phone.