hi, John
The number 30028555 should be HP HK support phone number, it doesn't match UC320 SIP trunk dial plan "3[1-9]xxxxxx", so you fail to dail it.
If the 2nd digit is 0, only the following dial plans are supported.
10[0-36]x.
108[138]
109
6xxxxxxx
90[1-9]xxxxx
900xxxxxxxx
8009xxxxx
We need to update our UC320 SIP trunk dial plan to support the phone number you dialed.
thanks,
william