Federated users can only be called or emailed

Hi,

I have several users (with external emails - Mail Users in Exchange, federated with my company) in AD with defined Telephone Number, so they appear in AddresssBook searches (WebSearch only, no local Contacts allowed). But then cannot be texted, phone icon is being displayed next to the name. When phone numbers are deleted presence status returns and they can be texted.

Any idea what can I do to keep phone numbers and have instant messaging turned on?

Thanks!