How long can a prepaid card last b4 it expires?

How long can a $18 prepaid card last before it expires? 3mths?4mths 6mths?is it the same for all prepaid cards from the 3 telecos?

thinkin to change to prepaid for some reasons.

any opinion on which prepaid card service is the best among the 3teleco?

i think it is 6 months, not sure

is it is starhub one, there is a number for u to call to check expiry

i think is 9 sumthing sumthing then 0000

inside the booklet have

180 days from the most recent top-up