If you want to claim a "Special Visit" Premium, you must claim an "A" Prefix Service Code (i.e. A065A instead of a C065A). You cannot claim a "Special Visit" Premium with a "C" Prefix Service Code. The OHIP Schedule of Benefits states this, however, it is quite vague: "For emergency calls and other special visits to in-patients, use General Listings when applicable."
On page GP59 of the OHIP Schedule of Benefits it says "Submit claims using the appropriate A Prefix assessment fee from the General Listings for assessment rendered in conjunction with a Special Visit Premium. What they mean by "General Listings" is the first section of your specialty's Consultations and Visits, which includes all of the "A" Prefix Service Codes.
Generally speaking, the only time that you would submit Service Codes that begin with the Prefix "C" is if you DO NOT intend to claim a Special Visit Premium (or if you plan to claim a Subsequent Visit, since these Service Codes do not have corresponding "A" Prefix Service Codes associated with them).