If you are being sued and you have 20 days to reply how likely is it that you can call the company and make arrangements to repay the debt?

Although it more than likely is a collection agency that has bought the account. You will need to deal with them not the original creditor. One of the factors that differ in 3rd part collectors and OC, is collectors often require payment in full. Some will only agree to a lump sum settlement. Much depends on what agency is bringing the lawsuit. Some are very easy to negotiate with, others it will be on their terms only. Still no one wants to go though the hassle of court procedure. It can't hurt to offer a settlement amount or ask for a payment option.