I am using voip with Vodafone as SIP peer for outbound telephony and i have a huge problem establishing calls to other people. It works like in
1 of 5 tries. The peer is sending SIP 480 temporarily not available. It took a while to identify this, because on the phone you just hear busy tone. On inbound calls i have not detected problems yet.

Calling to mobile numbers works better than to home/office numbers. If i use a different SIP Peer in same dialplan it works without any problem. If i connect a “all in one voip router” with vodafone peer it works without problem too.

Are they lowering availability if they detect Asterisk? Are there any IDs that can be changed, so they cannot detect the PBX ?

Are there any settings in Asterisk which affect timeouts or stuff like that?

Here:
http://voicent.com/kb/index.php/support/autodialer/581/sip-error-480-temporarily-unavailable they write:
“Depending on the exact cause of the error, your solution may vary. For example, you can try to add another VOIP account for different lines
(from the same VOIP service or different one), or slow down the calling
(by defining dialing intervals in Voicent gateway)”

What they mean with slow down and dial interval?

I have also the impression that the ISP resonds very quick with the error. Or has it even to do with the router itself? (i am using OpenWRT
and had a problem once with NAT-T after public ip change).

If i turn on qualify, the peer refuses also to answer (SIP read 403
forbidden). I was wondering, how Asterisk even knows that it is registered?

The register and peer status in Asterisk are both ok, i even monitor that in Nagios.

Its a big problem in Germany because the ITSP can force you by law to use their own branded router models, which of course dont use Asterisk. So if i would call them, the first answer would be, use a different router.