Hi,
I have been working with Cisco VoIP since 2001 and Asterisk and freepbx ,trixbox, elastix since 2007.
I'm very new to the site so trying to bid as low as possible and get better reviews as much as possible.
As far as the Questions you have asked , below is my take on these:
1. How to connect PBX to a mobile phones
You will need Smartphones with Android ,IOS, BlackBerry and some App for SIP connectivity.
2. Can the mobile phones use both PBX line and normal line
Yes you can use a phone for both.
3. Can PBX can be used for different companies.
Yes it can be but you need to have some customization.
4. Can PBX be integrated with a Mobile App
Yes it can be , it depends on the Mobile App.
5. Can PBX filter incoming and outcoming calls.
Yes that can also be done.
6. How many contacts can be managed at time.
As many as you like.
7. Can PBX be located in a different country of the dialer and how does it affect the quality of the system
Yes PBX and the phone can be in different countries , the call quality will depend on the Internet connection.
That being said I would like to have a little chat about your project to better understand the needs of the project
regards,