Is there a "universal network" that I can use on my iphone in different countries?

I will be traveling a lot this summer, I'm talking several continents. I'm wondering if there is any way that I can use my iPhone in all of these different countries? Is there any network that has coverage all over the globe? If not, how can I continue to use my phone abroad in a cost-effective way?

you can buy international simcards online or most company's sell bundles for international calls