Services can be broken into three parts.  First, you will add all the Service types available within your system.  Service types are categories you place Services into, for example, Labor, Features, Lines, etc. 

Next, you will add in Services.  These are the specific groups of items you provide, for example, Cell Phone Service, Voice Mail, Internet Service, Man-hours etc. 

Now, you can add in the specific Service items.  You can breakdown each service into individual items each with a specific serial number.  When used for an assignment, the service item is no longer available.  Alternatively, you can be general and add just one item to each service.  For example, with Man-hours, you can add 1 hour as the item and increase the quantity for the service provided.