Im new to this hobby, what is the "Two call system" Im reading about from other hobbyist?  What should I expect when I call a provider?

usually it's a place where the provider can see you or your car from her window.

When she sees you and knows that you are there and not a time waster and not driving a police car, then you make call number two and you get her address and room number.

It was a very popular method of screening out jerks in the old days of personal ad appointments, but not very common now.

The last few places I went to I just call and once i go to the apartment i call again and then they give me the room number and the code to prcess, but sometimes i park like a block away and they still give me  a code. DO they really check

and what common method is used now if not that? I know some do reference checking

Personal and work info, references and screening agencies like RS2K and Room Service.

Also smart gals check on various DNS lists that are floating around.

I'll occasionally do a reverse phone lookup as well. It can get expensive, but it's worth it when you have a date with zero references.

but what if you use a google voice number? I use google voice number i hope it isn't a problem for providers.

I use multiple methods to screen, and as long as I can get a reasonable level of comfort regarding the veracity of the info he has provided:

Then let's get in on!

If is just plain sloppy for a lady to give out her complete location in advance...  like asking for LE to show up!  
I have had ladies state when I called "I can't see you!"  I was at the wrong entrance.
You need to call about a minute before the appointed time...  no earlier...  but you should not be sitting in a car waiting, drawing attention to her location.  I like to find the location then back track to the nearest coffee shop, returning at the appointed time, call & go in.  She should give you specicific instructions...  like through the hotel lobby, elevators to the the right, rm # XXX.
skb