I've had to unfreeze to add one of our kids to our cell's family plan, to get some dental work done, etc., I ask who they use. Sometimes they have to call corporate, but I've always gotten it. I do a temporary unfreeze online for that agency only, you have a few options, at no cost and account is automatically refrozen at no cost.
Freezes are often free for senior citizens and anyone who was a victim of identity theft. A few states allow charges of $10; CT does and I think PA. A few states do not allow charges at all. And, the rest allow charges from about $3 to about $6.
Consumer radio talk show host Clark Howard's web pages:
http://clark.com/personal-finance-credit/credit-freeze-and-thaw-guide/
http://clark.com/personal-finance-credit/equifax-free-credit-monitoring-data-breach-dont-sign-up/
For those who don't click on links, Clark Howard has changed the name of his website to Clark.com, so start on his homepage and search for the topics that interest you.