SIP/2.0 488 Not acceptable here

Very often problem is with incompatible codecs.

Example:

Capabilities: us - 0x0 (nothing), peer - audio=0x906 (gsm|ulaw|g726|g729)/video=0x0 (nothing), combined - 0x0 (nothing)
Non-codec capabilities (dtmf): us - 0x1 (telephone-event), peer - 0x1 (telephone-event), combined - 0x1 (telephone-event)

<--- Reliably Transmitting (NAT) to 11.22.33.44:5060 --->
SIP/2.0 488 Not acceptable here

This line is important:

Capabilities: us - 0x0 (nothing), peer - audio=0x906 (gsm|ulaw|g726|g729)/video=0x0 (nothing), combined - 0x0 (nothing)

One end does not allow any codecs for this connection.

Enable some of these codecs: gsm|ulaw|g726|g729 and call should pass.