Hi Masi, 

It is against the terms of italki to share your contact details in discussions, but you might not need a group in Viber or other social network. Just create discussions in italki, and change your notifications in your settings so that you are messaged by italki for every response. 

I can offer these to you on skype as I have an English language chat group and live discussions there, if those would interest you. 

I am a beginner in this website and looking forward to a free discussion group in a mobile-based social network like Viber,... just for chat in this step, because I haven't any self confidence yet. So I prefer to take part in chats without any voice or video.
If there is anyone who can help me, It would be appreciated.
I don't know wether it is allowed to share my mobile phone?

Note: As a first step, you observe discussion and find out how others are participating and

responding by writing thier views and opinions.  Gradually, you can also share with your views.

Don't worry about mistake. Others who find your notes will/may correct it.

Better to choose sharing mobile phone as a final step.