I have a cisco UC520 that's working with a sip connection to the sip provider, this is running ios 15 all is working as intended.
I have another cisco 2811 cisco router running ios 12.4 that I'm having fun with.
my uc520 has extensions in the 201,202,203 and so on range.
my cisco 2811 has exntesions in the 41211, 41212 range.
Skills: cisco, security engineering, voip