I suspect a custom field with something like the following may work (note the number will need to be the actual suppliers of customers phone number).
<a href="tel:555-555-5555"><img src="path/to/phone/icon.jpg" /></a>
When Manager is viewed on a mobile phone than will call the number. On a Mac that will initiate a Facetime call. On other operating systems you will usually be prompted for your phone calling application.
or for a Skype call
<a href="callto:1234567">Call 123-4567</a>