Skype is currently only blocked over cellular networks. Voice calling using apps such as WhatsApp, Viber, and Telegram is completely blocked, even over regular internet links.

The TRA (https://www.tra.gov.ae/en/home.aspx) outlaws ISPs from allowing VoIP services. Obviously, the goal is to ensure that ISPs maximize their profits. Note that both ISPs - Etisalat and du - are majority government-owned.

Earlier VPN (which is illegal) was required to make Skype->Phone calls, otherwise the calls gets disconnected immediately after the other guy picks up. From last few months Skype->Phone calls are working without VPN in Etisalat elife connection.