Definitely call to add the unlimited plan, otherwise you will be charged at a per kb rate with is quite high. You can actually call Verizon now and have them activate the international plan for your dates of travel -- it will automatically start and stop on the dates you pick so there is no need to call again to deactivate it.

Texting costs 50 cents per outgoing message and 5 cents per incoming message. You can get around the outgoing rate by emailing someones text messaging address. (ie. for Verizon 2028805555@vtext.com)

HTSC is correct about the rate of $60 and ability to prorate.