DECT: No outgoing calls possible when extension name contains emoji

[pharmafirma]

Steps to Reproduce
Tested on event 36c3:

1. Login to your Guru3 account
2. Edit an existing, known working, DECT extension
3. In the "Name" field, enter an emoji, e.g. this lovely 🐈 cat.
4. Save changes, wait about 30 seconds
5. Try to call someone using your DECT phone

Expected behaviour
A call is being placed. The called phone rings.

Actual behaviour
The caller hears an error message "Die gewählte Nummer ist aktuell nicht vergeben" and the call is being dropped. The called phone does not ring.

Additional information

• The error only occurs on DECT. GSM or SIP extensions called 🐈 are no problem.
• Incoming calls (from other phones to the the 🐈DECT) are still possible.
• A more real-world example of 🐈 might be non-unicode names (Chinese, ...?)
• Since not even emergency calls (112) are possible, one might even consider this a critical bug.

[garw]

We debugged this on the last Congress and it seems to be caused by a bug in in Mitel's SIP-DECT software. We will see what we can do but a change to the Guru3 software cannot really fix this.