I'm on the first step for preparing a voip project in my business, how can you help me so I can start on good bases?

Thank you for your support, and to be well precie my first choice for voip solution is a Cisco solutionSo if you can help me in this approach i will be very grateful.Best regards  

Dear , VOIP systems are two types : free and paid free such as Elastix ,FreePBX,Asterisk .
Paid such as Cisco UC , Trixbox "new versions are paid versions " also NEC PBX Please note that for Paid PBX ,you have to buy the hardware to work on it execpt for Trixbox .
I actually tried all of them and Elastix is amazing for small amount of users up to200 users , so you can : a- get a server and create a virtual machine on it b- Install Elastix on the virtual machine c- create extensions ( for example extension:201 username: husam password:123 ...and so on) d- after that you have to configure a sip telephone to see the PBX and give it the extension configuration ( also there are software sip telephones and hardware sip telephones ) , software sip telephones such as Xlite and qutecom ,hardware such as Yealink ,polycom, grandstream snom and so on ...
This mean that you can on your laptop create the whole solution by building an elastix server on virtual machine and installing the sip telephone application on pc's inside the network and making them to communicate with each other without paying a cent.
but in real enviroment you should install the PBX on a server machine and buy a hardware telephones that will perform better and do the Job

use asterisk FreeBPX system is a very useful and sheep system note that its a open source

its depend on external lines and internal extensions needed and how many voip provider connection where u need to locate the pbx , how many remote users need to work , if u need to integrate ur systems using extend API ....