You can define whether mobile app users can add specific services to work orders by selecting the appropriate setting on the work order type level.
On the Work Order Types page, click the Wizard link next to the appropriate work order type.
On the Work Order Wizard page, click the Services link in the Form column.
On the Services page, click Allow or Deny in the Adding column next to the appropriate service, and then click Update.
For example, if a work order type is assigned to a service package with three services, one of which cannot be added...
...when you create a work order of this type you will be able to add only two services out of three.