Don't think there's any analog integration with the Redwood, such as sending the called ext. via DTMF separated by #, * etc. The Siemens 3000 had that to work with the Rolm Phonemail system. I also have a Redwood in my basement, was working as the home system until about 12 years ago. But I'm thinking, when I was with Rolm there may have been a customer with a Redwood and Phonemail, in fact I think it was a small IBM office. Maybe some kind of special software release was required.

For the message waiting - that was also an issue with the 8000 and 9751, don't think there was an analog code to do it.