Are you trying to register to testsip.net or to bsip.bestline.net ? Your ACL permits the hostname bsip.bestline.net but your registration is to testsip.net.
You also may need to allow the WAN to communicate with the Adtran itself both for SIP and RTP.
ip access-list extended allow-udp
permit udp any any
ip policy-class WAN1
allow list admin
allow list SIP
allow list allow-udp self
I generally find it beneficial to allow all traffic to self from the WAN, then use access-lists separately for administration and SIP applied to the protocols but this way should work.
"debug sip stack messages" as well as "debug firewall" may be useful.
I got it to work.
register 5125555555 auth-name "512xxxxxxx" password encrypted "xxxxxxxxxxxxxxxxxx"
authentication username "512XXXXXXX" password encrypted "xxxxxxxxxx"
this is what made it work.