AEM RTE will allow you, at first, to make a tel: link using a + such as this:
tel:+83493439343
This will work fine. No problems so far.
But, when you go and edit the same RTE component, the tel: link will be stripped from the editor and be removed completely when you next save the component.
This only happens when the tel: link contains a +. If the tel: link is just numbers or numbers and spaces this issue does not occur.
At first I thought this was a link checker issue, so I tried adding some regex and a special link prefix as seen here: http://experience-aem.blogspot.com/2015/05/aem-6-sp2-handling-custom-protocol-in-link-href-in-rte.html
I even added a tel:+ link prefix to no avail.
I have concluded that this must be an issue with the RTE but I can't seem to find a solution anywhere.