Does google voice on gmail charge if you upgrade your accout?

I started using the free version of google voice on gmail. It offered to upgrade me to where i can make a permenant number, voicmail, txt etc. Do they charge you to upgrade seperately, do they do it through your phone carrier if you give them your number or do they not charge you at all (i dont care about making international calls)|||well the call made by google with in US and canada are free for the year 2010 only...so u wont b charged if u make call in US and canada in 2010