I should mention that in 2014 my husband and I visited Slovakia (his home county). I had an iPhone 5 on Verizon and he had an iPhone 5S on AT&T. I put a Slovakia SIM card in my VZW phone and had instant connectivity. He put a Slovakia SIM card in his phone and it wouldn't work. It was locked and AT&T wouldn't unlock it, Why? Because he was on a payment plan that wasn't completed. So, yeah. AT&T and their GSM network is better.