I took another look at your debug logs -- I was wondering if my first suggestion was accurate (!). I also just noticed that in your first email, you wrote "Cannot call + +4935...9915", with two plus symbols - that's invalid.
In your call logs, I can see payload (audio codec) type 0 and type 8 in the SDP m=audio line of the SDP (Session Description file which is sent by Linphone to the SIP server, which describes what your handset is capable of). Interestingly, the accompanying rtpmap definitions are not listed in additional a= lines. It seems Linphone did not bother to send them, it just declares it can support those formats, which is probably OK.
For example, for a call attempted using either G.711-Alaw or G.711-ulaw , I would normally expect to see in the SDP:
m=audio 15010 RTP/AVP 0 8
PCMU and PCM8 (payload types 0 and 8) are defined in the RFC3551 standard, so perhaps Linphone just doesn't bother describing them again. I'm sure a Linphone developer would be able to confirm ;-)
In your call logs, for each call attempt, I can see your device sends a long list of supported formats (including the telephone-event ones for DTMF etc):
m=audio 7286 RTP/AVP 96 97 98 0 8 3 9 99 18 100 102 103 104 105 106 101 107 108 109 110 111
I can see the other device is only offering PCMU, PCMA and G.729 as formats it can support. That's OK.
The first difference between the bad and good calls: for the failed call, your Linphone offered 16, 22.05, 44.1 and 48 kHz sample rate AAC. For the working call, Linphone only offered 22.05, 32, 44.1 and 48 kHz sample rate AAC. However, it still offered the other AAC codecs, along with the older G.711, iLBC, Speex and iSAC codecs.
I think you are actually using G.711 for all these calls, so AAC-ELD 16 kHz enabled or disabled is actually a 'red herring'.
I also noticed in the OK call, you are calling
Via: SIP/2.0/UDP 192.168.254.71:49268;branch=z9hG4bK.xEZZuwbrr;rport
Are you prefixing "+ " in Linphone before the number? I would not do that, so clear any value of "Country code prefix" and also disable "Replace + by 00".
In the previous call which failed, strangely I think you were dialling correctly - with no space, i.e. +4935... .
From looking at the codec order of preference, I think your handset may have been using PCMU for the calls, and something else is going on.
I think what is actually happening is perhaps you should not include the + in the dialled SIP URI, because the SIP registrar is not recognising it. In the failed call:
"SIP/2.0 488 Not Acceptable Here [Media Descriptions Syntax error while parsing the SDP]"
However in the OK call, the SIP URI is
SIP/2.0 180 Ringing
NB the space! How do you have the number saved in your Contacts?
I believe PeopleFone may be seeing the dialled URI, seeing it has no leading zero, then using pattern matching to assume it is a German number, and ignoring the plus symbol as it is not part of the valid address@hidden format URI. Valid SIP URIs cannot have spaces in them; if so, this interpretation is clever by PeopleFone, but slightly confusing :-)
The number you are dialing is 4935xxxxxx26, this is a German number? Is it normally 035xxxxxx26?
Try enabling whatever codecs you want, but leave PCMU and PCMA enabled, then redial the number without any leading + or 00. PeopleFone's SIP server may be anticipating numbers dialled without leading zeroes, or perhaps your client is set up to incorrectly add/remove digits from a dialled SIP URI.
Make sure you have no prefix listed in the account settings, then try dialing "4935xxxxxx26".
Then try "04935xxxxxx26" (one zero).
Then try "004935xxxxxx26" (two zeroes).
If that works, try dialing "+4935xxxxxx26".
I would be interested to know what happens if you dial "035xxxxxx26"
Make sure to avoid any spaces in the URI. If that all works, something strange was going on before. If neither 0049 or +49 work in Linphone, I would suggest contacting PeopleFone support and asking if there is any known incompatibility with Linphone and their SIP service. I would also ask them to confirm whether dialling Germany from Austria requires any special country codes or prefixes, or if they have special dialling rules set up for Germany.
I'm interested to know how you get on...