Availability to clients? I 100% agree with Tom (and Ace, if most of your calls come in during the day, then you must do a ton of corporate business). In the 15 years I was a mobile, I received MAYBE 10 calls during the day for services. 99.9% of my calls came in after 6:00pm.
I think classifying yourself is just a way to justify your pricing (be it if you are full time or part time). Full timers can say "I have to charge this much because I am a full time DJ and it is my job" while part timers can say "I don't need to charge that much, because this is just a part time hobby for me".
Any experienced, qualified DJ (which most of us are here) will put the same amount of effort and time into every event they do, and will make sure their clients are completely satisfied. That is the only thing that matters, not a label.
And everyone thought the world was flat because that was the way it looked from their vantage point.
The fact is:
Brides call after 6:00pm because it's personal. Everyone else calls during regular business hours. It's also not unusual for Brides to do their initial shopping from work and call during their lunch hour.
In general, full time DJs are more likely to charge
less than part time DJs because their operation is more efficient. The more you work at something the better you become, the more you can combine efforts, and the lower your resulting cost of doing it. Furthermore, some things just die of old age NOT
wear & tear. Your mileage is always better on the highway than in the city streets.
A full time multi-op will always charge more than both part timers and solo full timers because they carry the single biggest expense of all -
Payroll.
A part time multi-op will always charge less than every one else because
there's no such thing as a part time multi-op. This is just a group of people fooling themselves into thinking they run a business.
Solo part timers will never charge less than what they would earn at their primary job. Those that
do it for fun most often charge next too nothing at all. It really is just for fun.
I don't think FT and PT DJs spend the same time and effort on clients, though the customer staisfaction may not vary.
The diference is that a full time DJ is more likely to have a consistent operational plan and support system in place that allows him to deal with more clients with less time spent per client.
While both PT & FT DJs succeed at satisfying their clients, the full timer is likely to serve
more clients per unit time than a PT DJ. He also has a wider schedule to play with.
What does it boil down too? Well, the full time DJ can structure his business to fit the number of hours in a comfortable work week. The PT DJ has to work a regular week (or portion thereof) - and then clock overtime to run a DJ business.
Part timers ALWAYS believe that Saturday is the only significant day of the week in the event business. The truth is it's the only significant day in the
family event business.
I teach by day and work on building my DJ business the rest of the time. I tell people that I'm a DJ first and a teacher second, but in reality I have to be good at both to feed my family. I've been around the block with marketing and running a business, but no matter how efficient I am, I would be more successfull If I were a FT DJ. There is a lot that needs to be done during the work day that I have a hard time getting done between 4-5 PM after school...not to mention having the kids and wife in the mix. 
PRICELESS