Advice needed on classes integration

Hi everybody,
in the application i'm writing (with VS2005) i need to make a call to a
remote modem,perform some analysis and filtering to the received
data,and,finally,insert the filtered data in a SqlServer database.
I am thinking to encapsulate all the call in a single "Call" object,which
will execute all the required steps.
So i have the following situation (i use tabs to emphasize the hierarchy):

call
{
actual call (which deals with serial port and gsm details)
data analysis and filtering
insertion of filtered data in the db
}

Each of the aboce entities is implemented as a different class (i wanna
test them separately),and all encapsulated in the call class.

After all this introduction,my question
So far i have written the code for the "actual call" and for the "data
analysis and filtering" in two separate class libraries.
Now i would like to create a class library for the call class,including the
two already written.Please notice that i would like to to be able to modify
the already written classes from this new class library i wanna create.

How can i do that?What i need is basically importing the existing class
library code in the newly created one...

Thanks in advance )