"Lync/Skype for Business will not attempt to normalize a number that already has a plus sign at the beginning"There are signs that this is no longer true, at least for customers running Skype for Business Server 2016 and the Skype for Business 2016 client. I was messing around with normalization rules last night and realized that my Skype for Business 2016 client (version 16.0.7030.1021 32-bit) WAS normalizing numbers that started with a plus sign.
This has all sorts of ramifications, all of them positive. That means that dealing with improperly formatted click-to-dial numbers in Internet Explorer is much simpler. We can now fix this with a simple normalization rule, instead of doing it in a trunk translation rule or route.
This also means that dialing contact phone numbers from Outlook can also be much more reliable, especially if an extension is entered. Before, if a user entered a contact phone number with an extension in Outlook using the "Phone number builder", it would format the number like "+1 (212) 555-1212 x 345". If you clicked this number, Lync would parse the "x" as a "9" and the number would come out in Lync like "+121255512129345" and would likely fail.
I have no idea how long this new behaviour has been available, and if it also works on the Lync 2013 client with current patches. I tried to see if I could change the destination phone number on an incoming call that started with a plus sign. It didn't work, so the MSPL workaround is still required as far as I can tell.
If anybody has any information on this or can test other versions of Lync server/client, drop me a line.