This excerpt taken from the VRSN 10-K filed Jul 12, 2007.
6. Migration to Extensible Provisioning Protocol Plan
Support of RRP and EPP:
Subject to this Section 6, Registry Operator will support the RRP as a thin registry. Registry Operator will continue to support RRP until all impacted registrars have migrated to EPP, but in no event later than 18 months after the deployment date of EPP unless otherwise agreed upon in writing by Registry Operator.
Dual RRP and EPP Operations: