Core Issue
If you verfy that the port works properly by connecting an analog phone on the same port and you receive a dial tone on the same port, then the issue can be because the VG224 is not able to provide proper voltage to the attached device.
Resolution
Issue the idle-voltage high command under the same voice port where you see this issue or where you attempt to connect the device. Refer to Ringing and Idle Voltages on Cisco FXS Interfaces for more information. Also refer the related document User receives busy tone instead of dial tone for troubleshooting the no dial tone related issue on the VG224.