Using Viber - port settings for plusnet router?

[#1]

I am trying to use Viber over plusnet wifi - I can connect, but the voice quality on my side makes it unusable. The friend I am calling has no problem speaking with other people, so it must be something to do with my connection.
Viber told me it was probably something to do with the firewall settings and the the following ports need to be open:
1) TCP 5242
2) TCP 4244
3) UDP 5243
4) UDP 7985

I have the Plusnet router (Technicolor TG582 N) with the settings it was sent with (I'm using Mac OS X so can't use the McAfee option that PlusNet provides).
I'm not really familiar with altering the settings - I checked the router settings online but have no idea how to make sure these ports are open or to set the router to allow this app.
I was looking in the "Game and Application Sharing" in the Toolbox (via http://192.168.1.254) but there is no option in the drop down menu that seems relevant to this issue.
Can anyone please help?

[#2]

You'll have to "create a new game or application" and choose "manual entry of ports".
For single port numbers just put the same value in for the start and end port.

[#3]

Many thanks for your help!