2 flavors linux with phone system in one hard drive but only using one linux at a time.... how?

I want to install freePBX in one partition and freeSwitch in other partion.
only one system would be used at a time. never will be both system running same time.

so my questions is how I can install both system but select which one i need to run in ssh.

so i dont know if there is a program or command that let me in the ssh client. give orders to system and tell what system i need if a or b

is this possible ? and if yes How.

I hope someone could drive me in the right direction

I think you mean to say Asterisk and FreeSWITCH…

I would have to say probably not. I think the best you could do is get two HD’s and shutdown and swap.