will this be part of my taxable income?

Hi all
A friend of mine signed a mobile phone contract with some agency and she’s now recommending this to me. I’m not too sure if I’ll have to pay tax for this sort of income:

she signed a contract for 1 year with monthly payment of $50(with $50 credit). she will get all her money back($50*12=$600) after 13 months. so it seems she can make free calls if she doesn’t overuse it. and how come she can get all her money back after 13months? that agency claimed that they would put the money into a trust account controlled by a financial company—that means even if the agency went broke my friend still can get her money back from that financial company. and how do they make any money? the answer is:
1) phone bills over $50
2) they sign a lot of contracts and thus put all the money into a pool and invest the money so they can earn money in 13 months

Does this sound fishy? if i do give it a go, will the money i receive after 13 months be considered as part of my income and therefore i have to pay tax for it?

thanks for your comment
Jess