My new job is heavily unified communications and Exchange centric, so a lot of my posts now will have an OCS/Lync Server focus.
Now that I use and rely on the Lync client to do my work throughout the day, I've come to depend on hot (clickable) phone numbers in emails and meeting requests just like web and email addresses. That way, all I have to do is click the phone number and it opens up in the Lync client.
To make a phone number clickable, simply preface it with the tel: prefix like this:
tel:1-415-555-1212 or tel:14155551212
You can hide the tel: prefix by inserting a hyperlink for a phone number which includes the tel: prefix, like this:
Be aware that hyperlinked phone numbers can be wrong or misleading! For example, this link for (415)555-1212 actually calls (650)555-4444.
If you see a phone number in Outlook where the sender did not include the tel: prefix, simply right-click the phone number, select Additional Actions, and click Call.