Interesting one this Andy.
Here's a screen shot of my phone from about 2-3 years back. My current balance is about £59.
Every month I buy £10 worth of O2 credit, they give me free text's, internet and calls for this.
I'm tight and hardly use my phone outside of my freebie limits. Hence the large balances.
I usually blow this credit whilst abroad. Use my phone like normal basically whilst on holiday. Calls to family, internet, etc.
Now:
I could also buy music, enter competitions etc, with this money from my phone.
Money I've already spent ??
This is starting to sound like a good idea. If me and our_lass stay within our limits each month,
we could top each other's phones up, thus never spend any money on topups ever again