I have a list of questions that i ask them when they inquire about my services, to make it easier to cater to their particuliar situation. (on the phone long before the session)
-asking them questions puts them at ease in believing you know what you are doing, and have control of your craft.
I then let them "think about it" for a couple days or whatever (without setting an appointment, usually)
-giving them this low pressure sales technique will cost you a few customers, as they may shop around, and get "sold" by a higher pressure shooter... That said, i still prefer it.
When they call back, they'll want to set an appointment, they will have a few more questions, and we address them on the phone. I gove them a few more details, and possible an outfit idea or two (I like families to all bring a white collared shirt for a matching shot, or couples to maybe wear matching color shirts... They actually like to be guided in this area most of the time)
By the time they come in, we both know how things are gonna go, and are comfortable talking and such because we have been on the phone quite a bit. This is very important IMO.
The questions I start with are something along these lines:
-What is the family situation? couple, young family, grown kids, extended family...
-What type of shots are you looking for? Artistic, formal, casual, business, etc...
-how many different poses/groupings? Kids only, solo headshots, girls only, etc...
-when was the last portrait of this group if ever?
From there, i ask a few sub questions and give them some info.
I also let them know if i have any resrtictions that might affect them... I hate having rambunctious kids causing trouble in my place... I can only realistically manage 3 of my muslins at one time, the rest stay on the shelf, and may need ironing before use
All in all, i'd say you should do whatever you can on the phone. it saves time with blocking out appointments. also, you may have to see them to show a portfolio to "sell" them, in certain situations... you cant do the phone all the time. In any sales, you need to understand your customers' expectations, and worries if they have any (so you can dispel the worries). Remember, in this situation you are 75% salesman and 25% photographer.
Just my $.02 hope it helps.