For those folks that have Snom M325‘s with older firmware (3.23), these steps might help!

To upgrade a Snom M325 from firmware 3.23 to a higher release:

1. You will need to use the TFTP method to upgrade to 324B12

TFTP Upgrade to 324B21 from 323

https://helpdesk.snom.com/a/solutions/articles/6000168259-how-to-upgrade-the-m700-or-m300-and-handsets-via-tftp

Binary Files

http://dect.snom.com/B324B21H324B21/M700/M700_v0324.fwu
http://dect.snom.com/B324B21H324B21/M300/M300_v0324.fwu
http://dect.snom.com/B324B21H324B21/M85/M85_v0324.fwu
http://dect.snom.com/B324B21H324B21/M65/M65_v0324.fwu
http://dect.snom.com/B324B21H324B21/M25/M25_v0324.fwu

Upgrade via PHP Script

2. After you have upgraded to 324, use the PHP script to upgrade to version 400:

Upgrading to version 400BXX from version 324BXX or earlier:

IMPORTANT NOTES

    1. Direct upgrading from version 324BXX to 400BXX is not possible, you have to update first to the version 355B25 and then to the version 400 to facilitate customers in this task we prepared an auto-update script at this address: http://dect.snom.com/324-to-400/auto-update.php , please follow the reported instructions.
    2. Rollback to version 355BXX or 380BXX is possible from version 400BXX

Upgrading to version 355BXX from version 324BXX or earlier:

IMPORTANT NOTES

    1. After upgrading to the version 355BXX you WILL NOT ABLE TO DOWNGRADE TO THE VERSION 324BXX. Please take this upgrade carefully
    2. The upgrade will remove all the manually uploaded contacts from the global address-book. Please make sure to re-upload the address-book after the update.
    3. In case you are doing the update from a 323 version you need to update to the version 324B12 before applying the version 355

Upgrade to latest Release Candidate

3. Once you have upgraded to version 400 using the PHP Script, you can upgrade to the latest release candidate 410B14

https://service.snom.com/display/wiki/DECT+M-Series+Firmware

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