Within a network environment, redundant capabilities for exchanging call-processing signals enhance reliability of telephony support for telephony endpoint devices. A data network, such as a telephony-over-local area network, provides primary support for the telephony endpoint devices, which may be telephony-enabled computers or Internet Protocol telephones. A second network has a first mode in which it is inactive with respect to telephony traffic to the telephony endpoint devices, but has a second mode in which call-processing signals are routed through the second network in response to a determination that the data network is disabled. As a result, telephone features such as call deflection may be continued when the primary support is disabled. In some implementations, the second network includes a third mode in which the voice information is also carried as a response to determining that the data network is disabled and the currently available bandwidth of the second network exceeds a threshold bandwidth level.