While those guys may be older or bigger, they don't seem to have any edge on you guys technically. So you may want to consider adding some of these to enhance the multi-ring feature (over time).
Of all those forms, I find the multi-ring the most useful. No need to hit a *72 or log in to a website. Just walk out of the house with a cell phone in your pocket, and later walk back in, and never miss a call.
So I am glad this is what you implemented first!
OBTW - With that previous experience I found no benefit from hitting a confirming keystroke to pick up the call. I could choose which device took the voicemail by setting that voicemail to answer more quickly (usually my mobile device). That way, I had the voicemail in my pocket as well.