Don't get into a long chat or discuss your services on the phone - these are virtually always timewasters who will never book. I get questions like 'So, what can we do during the hour?' - I tell them politely that I do not discuss my services on the phone and refer them to my website, although if they ask for specific information (do you kiss, do you do OWO, etc) I do answer even though it is all on the site. It never hurts to tell someone that they sound nice/friendly/have a nice accent either (I'm a sucker for Glaswegians) but don't be over the top - I only do it if it's true!
I get people ringing asking when I am available - rather than say 'January' or some such, I now try to bear in mind when the next time I want to take an appointment is and tell them that my next availability is then (clients quite often don't seem to have a specific time in mind, unless it's in the next hour).
If you know you are going to freeze, fake a bad signal/line and end the call - my hearing is terrible and I quite often do this. You can take a deep breath and call straight back (has to be straight away though) and sometimes just that split second really helps me to focus.