Has your current nanny resigned? I recall you posting about problems back in January.
Currently you haven't placed any ads but have responded to some ads placed by nannies - is that right.
Assuming so, what further information are people asking for via e-mail? Given that you have told them salary, working hours (thus also I presume details of which days).
Have you been sent any CVs or anything like that?
Depending on the number of applicants involved you may want to narrow them down before arranging an interview. It's a live-out job isn't it? Assuming so, where the nanny lives is going to be farily important as you will want them to be able to get to/from your home reasonably easily. So one thing you will want to know from the nannies, is where they live, how they would be getting to work (do they drive, will they drive to you, will they take a bus/train etc) - so you can see on a map what sort of journey they would have each morning and evening.
You will want to check early on that they meet any specific criteria you may have - for example, are they Ofsted Registered? Are they a driver and will they be providing their own car with appropriate car seats? What childcare qualifications they have, what experience they have with children of various ages. You will also want to confirm their right to work in the UK - so how long have they lived in the UK, what nationality are they, can they show you their passport, are there any restrictions to them working in the UK, can they show you a birth certificate, photo drivers licence, confirm they have a National Insurance number and a UK bank account (they do presumably want to be paid). You need to confirm what ID documents you will need to be seeing, so that they can bring them to the interview (if selected for interview).
Personally I hate telephone interviews, would always rather just meet the family (children included) so that everyone gets a chance to see how we all get along.