I have asked this question before however have had stabs at help from the community and no useful official help on this matter. As the Lync 2010 client gets deprecated (we have O365 and can now no longer add users using 2010 so have to upgrade to 2013 Basic) this is a more pressing matter for us. Original post follows:

We use Mitel UCA to initiate calls using our CRM and the callto: or tel: protocols. When you have Lync 2010 installed it steals the protocol registration each time you start up (same with Skype, however there is a check box in Skype to prohibit the association). This can be stopped with a regedit (which is absurd that it requires this kind of tinkering to STOP something from happening):

http://support.microsoft.com/kb/951868

We used to use Lync 2010 and followed this guide, but now some of us have upgraded to 2013 this trick doesn't seem to work.

PLEASE release a version of the client that has a simple check box to prohibit it from stealing these registrations (I say 'stealing' quite purposefully, though at the moment it feels more like a boat of pirates ransacking my protocol library) or at least tell me how to stop this nonsense.

Please don't point me in the direction of the link above - as I said it used to work, and now doesn't. Equally the following links don't help either:

http://social.technet.microsoft.com/Forums/lync/en-US/10ac1e4c-f991-43b6-b8e6-6996b1e2740c/disable-calltotel-link-registration?forum=ocsclients

http://social.technet.microsoft.com/Forums/lync/en-US/ab263247-78dc-470d-96b8-fe360bcf8701/lync-steals-focus?forum=ocsclients

http://social.technet.microsoft.com/Forums/lync/en-US/316f1416-92fb-4e03-9845-fdccd697992f/stop-lync-2013-from-stealing-tel-and-callto-protocol-registrations?forum=lyncvoice

http://social.technet.microsoft.com/Forums/lync/en-US/0deea245-d1eb-4aba-a22c-a5dce07aba15/calling-tel-callto-links-with-lync-2013?forum=lyncvoice

Does anyone have any advice? The regedit that I have pushed out is hit or miss depending on whether the user starts lync when they log on, or close it (it crashes) and reopen it.

Thanks in advance.

When you sign in with Lync 2010, Lync 2010 would modify the protocol so Lync 2010 can use the protocol via when Lync 2013 sign in, Lync 2013 would also change the registry key. Then Lync 2013 can use the protocol association.

I dont think this behavior can be changed. Seems most software would modify the registry when you need to.

You can try to modify the protocol association registry key under HKEY_LOCAL_MACHINE\SOFTWARE\Classes.

I'm sorry Lisa but, although this works periodically, it is a hack, not an answer (how can I unmark as answer?). If this continues to be an issue then we have no choice but to ditch lync and move exclusively to mitel UCA. If Skype (now wonder by ms) can provide a simple check box, why can't lync? Equally, the registry hack will only work until lync is restarted (which happens frequently) and there's NO WAY to stop it from taking the associations back again in 2013. I'm struggling to keep lync, my directors want to get rid of it, I am trying to champion it - but it's not doing itself any favours!