In the US a lawsuit is unneccessary. Simply inform the creditor that you wish to resolve the matter through written correspondance (snail mail). If they call back repeat the above, but this time add that further attempts to collect this debt over the phone will result in you filing a harassment petition with the Federal Trade Commission.
That usually puts an end to the phone calls, but if you don't actually address the issue the creditor will simply sell the debt off to somebody else. Your debt goes up and then somebody else calls you. Then you have to repeat the whole thing.
The best way to stop them from calling is to call them first. Have a calm conversation about how much you can pay. Take down the name of the person you are talking with and insist on dealing with that person alone. Pay something...even $5 a month will keep them happy. They might try to pressure you into paying more, but stick to your guns.
The big benefit of that approach is that it gets harder for them to sue YOU if you've made an effort to pay the debt.