Salary, can ask before interview, usually they will ask you instead , if not, will be normal the market price . Can also ask about weekly holiday and when do they need to take a leave before or during the contract. If terms match, then can meet in person
That's why from a simple phone conversation , you can already screen out someone that you don't like or even cant understand what she talks about although some really can't talk on the phone , you can ask them to call you when they are free.
This will save you some time too