here are two main causes for phones not to ring on incoming calls from your Manx Telecom landline.
PSTN Cable not connected
For your telephone to ring, you need to make sure there is a white telephone cable running from your Router\Adapter\Siemens phone to the ADSL filter\wall-socket. Without this cable, there is no way of ringing your phone.
We have found in several rare cases that certain models of BT Cordless phones are not compatible with some VoIP equipment, the same issue is reported with BT’s own Broadband Voice service. One way of testing this is by plugging in an alternative phone and trying that.
For futher information – please contact Wi-Manx Support.