Do I need to purchase the "Scout" system for each of the the other cordless handsets or will the main unit support the two cordless handsets? Anyone had a difficulty of keeping their phone numbers? Quality?
I have a similar setup that you do -- I have a base unit that has an answering machine, plus two cordless phones (one in the kitchen, one upstairs). I've had them for over a decade, and they worked on my old PacBell/SBC/AT&T line, my Comcast Voice, and now my Ooma. No need to buy the Ooma branded phones, if you don't want to.
Porting my phone number was pretty much hassle-free, if:
a) you've got all your documentation from your previous phone company (account numbers, etc.),
b) $40 (waived if you buy Ooma premier, which I didn't)
c) Two weeks of time to wait. Don't cancel your old phone service just yet. While I was waiting I hooked up an old phone to the Ooma for testing. Once the old phone started answering calls on my main number, I unplugged it and plugged in my cordless setup mentioned above, and it all worked smoothly, with no downtime.
Call quality is as good as my Comcast voice line, and probably better than my ancient POTS AT&T phone line. If you have a separate modem and router, Ooma recommends installing the box in between these two so that the Ooma has a direct line to the internet and can maintain QOS. We watch a lot of Netflix streaming around here, and I haven't noticed any loss of quality while talking and streaming simultaneously (this is on a Comcast "Blast" 20 Mb/s internet connection).
According to what I was paying for my Comcast voice line, I'll break even on the cost of the Ooma box in about six months. I'll let you know then if it's too good to be true.