Hi MCM, what your trying to achieve it totally doable and a regular requirement of crm. you can use the workflows feature to create and New Phonecall activity and there will be a button to 'Set Properties' of your new activity record
Subject - you can define text such as follow up call
Regarding - this should be set to the contact or account
Required - this should be set to the user
Start Time - you can generate the time based on the execution time and ammend
End Time - you can base this on the start time
You can set these fields by clicking into them, then clicking into the Dynamics fields section of the form assistant on the right to dynamics set the values of the fields.
If the Form Assistant pane is not displayed, click the Expand button Expand button.
Click the field where you want to insert a dynamic value.
Under Dynamic Values in the Form Assistant pane, from the Operator list, select a logical operator.
From the first list under Look for, select the entity or record that includes the fields you want to insert as dynamic values.
From the second list under Look for, select the specific field you want to insert, and then click Add.
If you want Microsoft Dynamics CRM to insert alternative values in cases when the field you specified in steps 4 through 6 is empty, repeat these steps to add additional fields, and then use the Move Up and Move Down buttons to arrange them in the order that you want Microsoft Dynamics CRM to evaluate them.
If you want Microsoft Dynamics CRM to insert static text when none of the fields you have specified contain any data, in the Default text box, type the text that you want Microsoft Dynamics CRM to display instead of a dynamic value.
Click OK.
The dynamic values appear as yellow boxes in the fields where you inserted them.
In the form for the entity, record, or conditions used in your workflow or dialog, click Save and Close.
In the Process Logic area, click Save or Save and Close.
Take a look at the following link to help to help you; www.powerobjects.com/.../how-to-create-automatic-follow-up-activities-in-crm-2011
you can also use the new Automatic record creation feature instead www.microsoft.com/.../set-up-rules-to-automatically-create-or-update-records-in-crm.aspx
I hope this answers you question, Kindly Verify :)
Best Wishes, Raz