You need to start from default configuration / out-of-box status or e.g. recover the phones from password loss? Here is how you can factory reset the devices:

Index:

A) Using the phones web interface

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1. longpress ( > 5s) Vol+
2. press Vol-
3. press Vol+
4. press Vol-
5. press Vol+
6. press Vol-
7. press SpeedDial Key 1 [BS1]
8. press SpeedDial Key 2 [BS2]
9. press SpeedDial key 1 [BS1]
10. if completed you will notice a short confirmation sound and the device will reboot, if not managed ( e.g. by provisioning) it will come up on factory default state as desired.
    
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HD350W & HD351W

1. Dial: * 9 9 0 0 0 0 #
2. if completed you will notice a short confirmation sound and the device will reboot, if not managed ( e.g. by provisioning) it will come up on factory default state as desired.

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1. Short press for less than 2s to reboot the phone (base)
   or
2. Long press for at least 10s to restore to factory defaults in Static IP mode and then reboot phone (base)

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