Set the Reserve Time checkbox to False for Logged Phone Calls and to True for New Phone Calls through Workflow

To create the Workflow:

 

1. As an Administrator, navigate to Customization > Scripting > Workflows > New
2. Enter a Name, for example "Set Reserve Time for Phone Calls"
3. Set Record Type = Call
4. Set Execute as Admin = True
5. Set Release Status = Released
6. In the Initiation section, mark Event Based
7. In the Event Definition section, mark On Create
8. Set Trigger Type = Before Record Load
9. Click Save
10. Click New State
11. Enter a Name
12. Click Save
13. Click New Action
14. Click Set Field Value
15. Set Trigger On = Before Record Load
16. In the Condition section, mark Visual Builder
17. Set the following in the Condition field:

Field = Status
Compare Type= any of
Selection = Completed

18. Click Save
19. In the Parameters section, set Field = Reserve Time
20. In the Value section, mark Static Value
21. Set Checked checkbox = False
22. Click Save
23. Click New Action
24. Click Set Field Value
25. Set Trigger On = Before Record Load
26. In the Condition section, mark Visual Builder
27. Set the following in the Condition field:

Field = Status
Compare Type= any of
Selection = Scheduled

28. Click Save
29. In the Parameters section, set Field = Reserve Time
30. In the Value section, mark Static Value
31. Set Checked checkbox = True
32. Click Save

Note: This can be an alternate solution for Enhancement 114731 - Lists > Relationships > Entity records (Customers/Prospects/Leads/Vendors/Contact/etc.) > General tab > Activities subtab: Ability for the Admin to control the default value for the "Reserve Time" box when logging or creating new phone call.