The person going to confession and the priest hearing that confession must be in the same physical place. It is not possible to celebrate this sacrament by phone, letter or e-mail.
Why not? Although in one sense the Sacrament of Reconciliation is a private act (we do not mention our sins before a group), in another sense it is a public act (we have all sinned and we all need forgiveness). The reconciliation intended by this sacrament is twofold—with God and with the community of believers, as well as the larger human community.