Cisco 881 SIP

Hey

I have a problem with a Cisco 881 Router, we have 2 phones on it, they at making a SIP connection to our phone provider. but half the time they are unreachable by the phone provider, becouse they dont answer in 2000 miliseconds, any one els have had this problem? and know what to do

Kind Regards

I have the same issue with UC540 system where inbound calls fails, did you manage to get a fix for this?