Are we charged for using the voice / calling services?

Yes. The mobile networks charge us for those calls, so we count them against your message / segment credits.

The cost for Voice Forwarding is 1 Message/Segment Credit per minute. 

The cost for Click to Call is 3 Message/Segment Credits per minute.

Mosio has Voice Forwarding and we now offer Click to Call for Basic and Plus Plans. You can choose to forward phone calls to your texting number to another phone number (office phone, for example). The cost for Voice Forwarding is 1 Message/Segment Credit per minute. The cost for Click to Call is 3 Message/Segment Credits per minute.

Article: Do you offer voice services as well?