I need to use a key pad when I use the phone
I wonder if you can find a touch-tone tone generator pad and just hold that near the mirror. Such gadgets were available a few years ago and were designed to be held against, say, a pay phone, so you could carry your own auto-dialer.
OnStar's slant on the phone seems to have changed. They now emphasize its greater power, longer "battery life", and hands-free access compared to a handheld, where they used to emphasize using it as your primary mobile phone.