Are restrictive endorsements to settle debts valid in Mass. Other Debt

It can be done, but its often ignored, or the check is returned.
In this case, the state that would govern the contract terms is stated in your agreement with AT&T. That might mean DE, NV, TX, or NY, just guessing and too lazy to research it. You can.

I suggest you avoid taking a settlement by any debt collector. It won't really help improve your credit score, its already been written off by the merchant, then the contract is sold for pennies on the dollar to the debt scavenger who tries to make money off of your guilt. If the debt was for $500, they might offer you a settlement of $200, after having bought the debt (in bulk) for maybe 10 cents on the dollar, often 3 cents on the dollar.

Your call, boss, but that deal might not even be legitimate if the SOL in your state has tolled. That would normally be the last time you made a payment or racked up a charge on the account.

 

If you do decide to settle, be sure to get something in writing that this will be payment in full for the debt.