So it looks like you are using SIP, either trunking or devices. These errors seem to point to a network issue at first glance, by the 'unable to send message over network' comment, but then I see a 'Out of Memory' comment as well.
From these I would say that you are not getting a lot of these, as calls would not be connected as no ack or invites are being sent across the network.
have you got anyone complaining that calls sometimes are not connected? Unfortunately, these errors do not provide further information about the call.