* find all the requests issued before the start of the grace period, indicating
  channels which should be considered for recycling (b/c their grace
  period has passed)
* make lists of redeemed and unredeemed channel phone numbers, where
  "redeemed" channels have been used since the start of the grace
  period, and thus should not be recycled
* return them to the caller for processing (ie: we will defer actual
  recycling to the `registrar` level)