I too have a GoPhone with ~$350 in balance. I wonder if I can transfer the balance to a post paid plan. Sign up for 2-year and a free phone at the same time. And use the transfered balance to pay for the ETF?
I have the same question. My prepaid sim will expire, and I will lose the credit.
I plan to make a habit of this, so I would like to find ways to use this credit (obviously other than making useless calls).
You can buy ringtones and programs for your phone using the credit. at&t's MediaMall, Nokia's OVI Store and (I believe) Android Market accept carrier billing as payment and that should come out of your prepaid balance. You should also be able to do the donation SMS, like to the Red Cross, and have it come out of your balance.
Other than that, there's attempting to move the credit to a new postpaid account (YMMV there).