From my experience, a lot of institutions mail a letter so they have it in writing as proof. Some make calls either in conjunction with a letter, or as the sole notification - but if you do that, you need to have a good log to prove the notification took place.
As far as the formal requirement, Reg E just requires notification, which could be oral or written. The technical requirement is found in 1005.11(c)(2)(iv).
"(iv) Reports the results to the consumer within three business days after completing its investigation (including, if applicable, notice that a provisional credit has been made final)."
The CFPB exam procedures provide a bit more clarity on the option of notification being either written or oral:
"The financial institution must provide within three business days of the completed investigation an oral or written report of the correction to the consumer and, as applicable, notify the consumer that the provisional credit has been made final (12 CFR 1005.11(c)(1) & (2)(iii) and (iv))."
All of that said, keep in mind that if you are revoking the provisional credit, written notice is required under 1005.11(d).
Adam Witmer, CRCM
All statements are my opinion, not those of my employer, and should not be taken as legal advice.www.compliancecohort.com