Thank you both for your answers. Actually I think you are right and the displayed passcode is not correct.
I have tried to reproduce the hashcat format of that hash here and it worked :
https://sites.google.com/site/httpbrute/tutorial
--> $sip$*192.168.1.110*192.168.1.110*user151*Apple*REGISTER*sip*192.168.1.110*5060*b57aa7088ae5cac88d298d66f2c809cd****MD5*77795e92300dcc3c2fd974b2b47e5f0c
--> hashcat -m 11400 -a 3 brute_test ?l?l?l?l?d?d?d
[...]
$sip$*192.168.1.110*192.168.1.110*user151*Apple*REGISTER*sip*192.168.1.110*5060*b57aa7088ae5cac88d298d66f2c809cd****MD5*77795e92300dcc3c2fd974b2b47e5f0c:pass151
I have tried to reproduce the hashcat format of that hash here and it worked :
https://sites.google.com/site/httpbrute/tutorial
--> $sip$*192.168.1.110*192.168.1.110*user151*Apple*REGISTER*sip*192.168.1.110*5060*b57aa7088ae5cac88d298d66f2c809cd****MD5*77795e92300dcc3c2fd974b2b47e5f0c
--> hashcat -m 11400 -a 3 brute_test ?l?l?l?l?d?d?d
[...]
$sip$*192.168.1.110*192.168.1.110*user151*Apple*REGISTER*sip*192.168.1.110*5060*b57aa7088ae5cac88d298d66f2c809cd****MD5*77795e92300dcc3c2fd974b2b47e5f0c:pass151