Pre-Paid Phone With Bonus Min. Can I TXT RS Membership?

[King3vil]

okay so i recently received 500 bonus minutes on my LG pre-paid cell phone due to a mix up by LG. okay so i got 500 bonus minutes and when i check my account information, it says this:

1) Cash Balance: $0.00

2) Bonus Minutes: 500

so my question is if i buy runescape membership through the "Subscribe By Phone" method which cost $7.99 for 1 month, since its a prepaid phone with bonus minutes, will my cash balance go negative?

And what if i use the the "Subscribe By SMS" method?