A method is provided which relates to online charging within an IP Multimedia Subsystem, IMS. The method comprises at an IMS charging node (30): (a) receiving (S-C) a credit control request message from an IMS service network node (20) over a service charging interface (22) provided between the IMS service node (20) and the IMS charging node (30); (b) determining (S-A; S-D) with reference to one or more triggering conditions that an announcement is to be provided to a user associated with the credit control request message and/or another user; and (c) following such a determination, initiating an announcement service in the IMS service node (20) by sending (S-E) an announcement request in a credit control answer message over the service charging interface (22) to the IMS service node (20), the credit control answer message being in response to the credit control request message, and the announcement request comprising announcement information relating to the announcement to be provided.