How do I change Sender field on campaign phone call?

Hi,

i've just created my first campaign which has a phone call activity as one of the campaign activities. I wanted to make the Telesales team both the Owner and Sender of the activity. When i distribute the activity i can assign the Owner as the Telesales team and add the activities to the Telesales queue however the Sender field is greyed out in the New Phone Call form and when i hit Distribute it populates my user account as the Sender on all the calls and drops 5000 phone calls into My Activities.

How can i change the sender to not be the person setting up the campaign?

Thanks
Craig