Increase ability to route calls to agents

We would like the ability to set an agents or a group of agents as the default for incoming calls. (Ex. if the agent is not currently on a call, they will receive any incoming calls first.) We want to leave other agents on call as an overflow group so that we don't miss any. We also want this default group/agent to be flexible. We want the people in the default group to be able to change on a weekly or daily basis-- or according to a set schedule.