There's really two options since most of their calling will be back to the US, and not local.

1) get a local SIM with data (1GB will get you quite a bit of calling, if you don't use it for anything else), and use Google Voice as mentioned above. Forward your US Verizon numbers to the Google Voice number before you leave the US.

2) Pay the $10/day on Verizon. It's more expensive but covers local calls and calls back to the USA (which they likely have unlimited amounts of, if on a recent plan). Also no 2nd number to hassle with.