Does it cost $ to change phones on Verizon?

I will be getting an iPhone soon. Right now I have an old, really rugged phone. When I get my iPhone, I will be sort of scared of breaking it when I am outdoors doing canyon adventures when I'm jumping around and falling and sometimes going through water. So what I want to do is activate my old phone when I'm going somewhere where my phone will get a beating, then activate my iPhone when I get back. Does it cost money everytime I switch my phones on my line, not the data plan but is there an activation fee everytime?