Help with notifications

Hello All-
My company currently has a T1 line as its major connection to the Internet, and a cable modem for backup when the T1 goes down. I have set Nagios up to monitor the T1, but I’m not sure how to set the notifications up so that they are sent via the cable modem rather than the T1 when the T1 goes down. I need to send the notifications to a Verizon cell phone, which I can do via vtext. I am using Postfix as my MTA. I’m relatively new to Nagios, and am very confused about this issue. Any help, or push in the right direction would be greatly appreciated. -Thank you