Yeastar S20 PBX blocked ports -- 2

Job ID: 36952411

Budget: $10 – $30 USD

i had 2 Yeastar S20 PBX in different countries
the problem is between the 2 countries is blocked port's so the voice is not stable and you can't hear as well ,,
we are using linkus for calling not VOIP phone ,, so is there solution as openvpn or something else ?
thanks
Related categories: Asterisk PBX VoIP OpenVPN