Good afternoon,
Would a letter to a customer regarding a line of credit already established and with the intent to encourage the use of the line be considered advertising? The letter contains specific information (such as account number, the current rate). In this case would the APR still be a triggering term if the information is account specific? Thank you!

If it is to a specific customer (1), then no. If it is a letter that will be mailed to numerous customers, then I believe it is an advertisement. Read the definition of "advertisement" in the Commentary to §226.2(a)(2). Be sure to read the Examples (section i) and "The term does not include section (section ii).