I work as a Ligitation Manager for a Loan Servicing Company and Collection agency.
Firstly, do you know the date of delinqnecy on the debt (when was the last time you made payment)? Your credit report should show it.
That's kind of where it becomes tricky and you might have more options than you thought - but might not understand the ramifications of them.
If it's really old - say almost 10 years old? - then the statute of limitations on it will run out and the CRA's (Credit Reporting Agencies) will just drop the tradline form your CBR.
If it's not that old, and you settle it - CRA's typically mark the tradeline on your CBR as "settled and closed or a lessor amount." Now, although it's closed, the tradeline is still there. Some creditors may perceive this as "She took services and then only paid 50% back."
With that said - you can also pay it in full - but again, it will still show on your CBR for years as "Collection Account Paid", or a P9 account status code.
Maybe try this first - contact the cell phone agency or collection agency their using. Block your caller ID (or they'll document it and then start calling you about it since they know your number.) Speak to a member there and try to negotiate that if you paid the entire balance, in full, over the phone (via debit card,credit card, whatever), then they woudl agree to COMLETELY remove the entire tradeline. I'm sure many will say, "No No No, we cant' do that - it violates the FCRA." - So, wait until the last full week of the month when every agency is scrambling to hit their goal - call in and offer it again. But before you pay - GET THE AGREEMENT IN WRITING!!!!! Then pay it over the phone, and hopefully if they do stay within the lines of the law as our company does, you'll see it disappear in a matter of 30-45 days.
Hope that helps in some way.