Allow multiple IP address to be "IP lockdown"ed to in the VoIP Outbound Security settings

At home, I have two ISPs (one being VirginMedia just in case BT's exchange "goes down") and therefore have two IP addresses. I also have VoIP on my mobile phone which connects when I'm in the remote office (third IP address). However, the "IP Lockdown" function in the VoIP system will only allow a single IP address to be set and I don't want to have to modify it every time the route switches connections or I have to go into the office. Can the lockdown system support a comma-delimited list of IPs?