(a) The address and telephone number required under this part shall be the independent contractor's official address and telephone number for purposes of the Act. Service of documents upon independent contractors may be proved by a Post Office return receipt showing that the documents were delivered to the address of record or that the documents could not be delivered to the address of record because the independent contractor is no longer at that address and has established no forwarding address; because delivery was not accepted at that address; or because no such address exists. Independent contractors may request service by delivery to another appropriate address of record provided by the independent contractor. The telephone number required under this part will be used in connection with the proposed penalty assessment procedures in 30 CFR part 100.