We definitely want to make sure that you have all the information you need before making a purchase and are happy to help out. The Wireless Home Phone will work with both corded and cordless phones. For corded devices to receive service they would need to be connected directly to the device and connecting to a local wall jack would not transmit service to the rest of the home. However, if you have a cordless phone that comes with additional handset receivers, they would be able to receive calls as long as the main cordless phone is connected to the Wireless Home Phone.
In regards to the security system it may not be compatible with certain home security systems. So before purchase you'll want to check with your home security system provider to confirm the compatibility requirements of your system. Reviewing the manual and specifications we do not see any current method to adjust or change DTMF tones.
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I would advise against using a cellular service for monitoring a security system. In the commercial world, POTS lines are still needed unless a system was designed to use an alternate means.