We just endured a two month period with really bad DSL service. My Ooma had all the symtoms you read about here - dropped calls, warbling, stuttering, calls not completed, etc. Speedtest results were variable. Sometimes pretty good, and then just awful. Modem resyncing 5 or 6 times a day, at least.
Getting DSL service back to normal was quite the ordeal. Some of the gems from ATT during the many happy hours spent on the many service calls:
"Your service checks out fine. No problem here - must be your equipment."
"Wow, these are really serious line quality problems"
"Apparently, someone has stolen your password, and many people are connecting to your account. That's what's causing all your dropouts" (seriously)
And my favorite, "there, we fixed it"
I could go on. The point is, with the ISP problem fixed finally (fiber optic feed, so I'm told) our Ooma works perfectly. Absolutely flawless since the repairs. All problems gone. Before ranting about Ooma, maybe the first thing folks should do is make sure their internet is working as it's supposed to.