Port 1 needs internet access to build the VPN tunnel back to Calltower. Preferably this is connected directly to your ISP and not behind your firewall. If there needs to be a static IP assigned on the ASA for this to work, contact Calltower to assist with this.
If the ASA does need to be behind a firewall (less desirable), please ensure that port 500 and 4500 are open to 188.8.131.52 and that it has internet access.
Port 2 needs to connect to the voice vlan to connect to the phones.
Below is an example of how the switch port should be configured if you are using a Cisco switch with voice vlan 2:
description uplink to ASA port 2
switchport access vlan 2
switchport mode access