That sounds great!
Manually highlighting a number may be a good idea to implement in a later version, I would think that only 5% of users may use it. Google Voice doesn't implement it, although they do give you an option if you click the extension to manually enter a number, just like you can in FOP2.
Also, for my case, I am not sure how much I would use call notifications. I would use the extension primarily for initiating calls, so in my opinion I would focus on that experience first.
The icon to show if you are connected or not is a good idea and can be very valuable.