I had an account with Sprint PCS back in 2003 and I was tricked when I asked about a new plan and a salesman got me on the plan with out my authorization. That put me on guard and when I finished the plan I quit Sprint; To make sure they don't trick me again a call two different persons wich told me that every thing was okay with my account.
Three months ago I checked my credit and got stonished that I have a debt in collection.
The guys in Sprint don't gave any explanation even though I spoke to three of them all ready.
What can I do?

You should contact the agency, request proof of the debt and of their ability to collect it.

Just be aware that once you initiate contact, they will request updated information so they can continue in their efforts to collect the debt.

Unless you obtained something in writing from Sprint, you will most likely end up being responsible for the charges they have placed in collections.