We get so many frivolous disputes through the call center. Can we ask them to put the dispute in writing before we will begin our investigation. Hopefully this will cut down on the number of ridiculous disputes.

I am making the assumption that you are asking about direct disputes regarding information being reported to a consumer reporting agency. Think the first sentence in the information below taken from the Federal Register published July 1, 2009 beginning on page 31484 answers your question.

(c) Direct dispute address. A furnisher is required to investigate a direct dispute only if a consumer submits a dispute notice to the furnisher at:
(1) The address of a furnisher provided by a furnisher and set forth on a consumer report relating to the consumer;
(2) An address clearly and conspicuously specified by the furnisher for submitting direct disputes that is provided to the consumer in writing or electronically (if the consumer has agreed to the electronic delivery of information from the furnisher); or
(3) Any business address of the furnisher if the furnisher has not so specified and provided an address for submitting direct disputes under paragraphs (c)(1) or (2) of this section.
(d) Direct dispute notice contents. A dispute notice must include:
(1) Sufficient information to identify the account or other relationship that is in dispute, such as an account number and the name, address, and telephone number of the consumer, if applicable;
(2) The specific information that the consumer is disputing and an explanation of the basis for the dispute; and
(3) All supporting documentation or other information reasonably required by the furnisher to substantiate the basis of the dispute. This documentation may include, for example: A copy of the relevant portion of the consumer report that contains the allegedly inaccurate information; a police report; a fraud or identity theft affidavit; a court order; or account statements.