When you hit the phone icon to dial, the phone goes ‘off hook’
This gives a dialling tone.
Although this may indicate you have a connection, I find it annoying, especially when I am trying to dial an IP address for a VC unit. After all, what VC units gives you a dial tone?! The same is true for a mobile phone.
As yo press the keys you get a tone - but not when you use the backspace key. bug? Cisco units give a tone on backspace.