Correct my sentences please.

#1 is fine. I have no idea what #2 means.

I just wanted to ask how much currency do you have on/in your vodafone. Here do we use in/on

2. He is becoming/getting fat. Will both do here or its wrong to use getting here.

Thank you.

2. Both are fine.

I have no cellphone, so I don't know what people say about that. Don't you just get an invoice at the end of the month?

I am using a prepaid connection. So i don't get invoice.

Thanks

I'm not really familiar with this way to use a cell phone, but "How much time do you have left on that one?" or "How much do you have left on that number?" would work if both people understood the context. I would be clueless.