I have such problem ..
i try to call somewhere to PSTN from my cisco IP Phone 7960
connection established .. and i can speak and hear other side ..
next moment i drop the line .. and redial this number again
and i see .. "connected" status on my IP phone but can't hear other side
and other side also can't hear me again ..
next few times i 'm trying call this number again and .. sometimes can hear otherside .. sometimes not ..
we use CCM 3.2.2c with hotfix F and cisco 5300 gateways
problem dos't depend if i use NAT or use real IP addres onmy ciscophone