I have a few SPA112 in the field that work great for faxing and analog phones.  However, I have a devil of a time getting them to work with alarm systems from Tyco, etc.  Supposedly the alarm systems simply need dial tone to dial out but they just do...

I have a UC320W with the latest firmware loaded that has been having trouble from day one with a particular line disconnecting properly.  At times one line will stay connected indefinitely until it is either unplugged or the phone system reset.  Obvi...