I have 18 remote locations with Sonicwall's running cisco phones off a UC520. I have found that SonicwallUC520 is very unreliable becouse of routine dead tunnels and the the US520 would not support IKEv2. I ended up doing sonicwall to sonicwall with a NSA 5500 at the head end and connecting to the UC520 on the LAN side from the NSA5500. You will need a NSA240 or higher at the headend, the 180 does not support virtual interfaces to trunk the UC520's multiple VLANS plus routing rules to get CUE 10.1.10.0/30 traffic
My two cents!
Dave