ActionTypes.OpenUrl in ThumbnailCard with "tel:" URI doesn't open call in Teams Desktop Client

Question

Our Microsoft Teams bot answers searches for contacts return a ThumbnailCard containing the name, picture and an ActionButton (Type OpenUrl) for the users to be able to voice call this contact.

Phone number format used is tel:+4314023596 which should be proper for this URI schema.

There's an inconsistency in which situations that works

Working:

• Using the Teams iPhone app, the phone opens the "call this number now?" dialog

• Using the emulator on the desktop, Skype for Business is properly opened with the correct number passed to the application

Not Working:

• The Teams Desktop client ignores the very same ActionButton by doing "nothing" when clicking on it.

• The Teams Web Client opens a blank page, in the console it returns the error Invalid URL received: tel:+4314023596

Goal is that on every device and client the default way on how to place a voice call should be placed. Any hints please what I'm doing wrong?

Here's how I build the ActionButton, cleannumber is a valid phone number without spaces and parenthesis, starting with +<countrycode>.

CardAction ca = new CardAction()
{
    Type = ActionTypes.OpenUrl,
    Title = "Call",
    Value = "tel:" + cleannumber
};

Answer 1

Unfortunately, this is not supported for Desktop client and browser right now. This is part of our backlog.