With the new residency rules I am not sure you are allowed to take call by the week - because even with home call you are required to have a certain number of days off and a certain number of hours free of call responsibilities, no matter even if you were to request this. Thus, when on call for a weekend one resident cannot be on from friday 5pm to monday 8am continuously.
Perhaps some programs get around this but I am not sure how they can do it legally. Thus, call is by day/night.