Purchasing items with cash before filing for bankruptcy?

• accept credit card online
• internet credit card processing
• credit card settlement
• cash secured credit card
• credit cash
• accept credit card payment
• credit online payment
• credit card payment processing

I know its bad to purchase "luxary items" within 90 days of filing for bankruptcy with a credit card. But what about cash? Ive been saving up money for a new phone from T-Mobile and I finally have enough for a new smartphone but my mom (I'm 17) is scared of purchasing it for me because she believes her upcoming case. She isnt going to bankruptcy because of credit card debt but because a few years ago she signed for a car for a friend and she decided to stop paying for it.. Would getting a phone & paying the monthly charge with T-Mobile effect my mother in any way? Of course I wouldnt want to get her in any trouble if so.

Purchasing items with cash before filing for bankruptcy?