Displaying Call Duration on Mitel handsets

[VinceWhirlwind]

I've looked through CoS options and can't see anything relating to enabling this.
My handset doesn't display any call duration timer, but some other people tell me they get a call duration in whole minutes.

[petr.necas]

My understanding is that Mitel phones show call duration only for external calls (in HH:MM format), for internal calls they do not show call duration.