I have read about Lightning voice, where you can make/receive calls based on yearly subscription. If that is the case, Will it be an alternative for the traditional CTI integrations happens in Salesforce? What is the main difference between going with lightning voice and CTI integration.
The main difference would be that Lightning Voice Setup doesn't involve any hardware except for your internet/network and phone hardware to your desktop machine. It's essentially a Soft Phone solution provided by Salesforce that's similar to having Google Voice number (assignable) where you use it in conjunction with your Salesforce instance.
Everything is configured using permission sets. Like a CTI integration, there are widgets and toolbars. It's essential that your network have the capacity to support the extra bandwidth the telephone calls will need if you're going to go this route. The other thing to remember is that outbound calling with Lightning Voice is currently only available in the US and Canada.