19:31:40.065489 IP (tos 0x68, ttl 64, id 2311, offset 0, flags [DF], proto UDP (17), length 32)
arch-desktop.sip > 192.168.55.8.sip: [bad udp cksum 0x0579 -> 0xb8de!] SIP
0x0000: cc2d e007 66bf 9a4d a5eb e450 0800 4568 .-..f..M...P..Eh
0x0010: 0020 0907 4000 4011 2c03 c0a8 4d02 c0a8 ....@.@.,...M...
0x0020: 3708 13c4 13c4 000c 0579 0d0a 0d0a 7........y....openssl enc -aes-256-cbc -pbkdf2 -iter 1234569 -salt -in .xfree_aliases -out .xfree_aliases_encryptedShort answer : There is no solution as long as you are using Linux and a Bluetooth headset.
Long answer: For music playback only A2DP is suitable, but it does not have an INPUT mode so use of the headset for VoiP isn't possible. The HSP/HFP mode uses the CVSD codec which is sampled at 8 kHz, same as used in telephony systems (so sounds like an old telephone, if at all).
A fix was introduced in pulseaudio 10 for automatic switching between A2DP and HSP/HFP profiles, based on detecting that some phone application wants to access the microphone or not. But this doesn't work for all headsets and applications.
You may read the long-running bug-report Bug #508522 : Add automatic switching to HSP/HFP from A2DP when a mic is needed, starting in 2010 (!), and whose status today is still "New" after having been closed and re-opened during its long history.
Such headsets are reported as working perfectly well in Windows and MacOS, so the problem is only with the Linux pulseaudio implementation of Bluetooth. You would need to use a USB headset to avoid the problem.