Hi Kate,
I have no idea if is it anyway possible to do this kind of telephone verifying in Marketo, but as we are mainly Salesforce Consulting I know that there it is possible to do a further verifying where every number is shortly called to check if it "exists". If you need this, maybe I would take a look at AppExchange.
For the email address you could take a look at javascript (if you implement it into Wordpress anyway) to check this. Just take a short look at this discussion from a few days ago: https://community.marketo.com/MarketoDiscussionDetail?id=90650000000Ppy4AAC
This part blocks mail domains which are not wanted:
var invalidDomains =
[
"hotmail.com",
"yahoo.com",
"aol.com",
"gmail.com",
"msn.com",
"comcast.net",
];
But you can also do some other stuff using javascript. But, and this is just my opinion and experience, if people don't want to give their real email address they find a way (a lot of trashmail offerings exist...) so I prefer to build up data management campaigns which prevent your database to be flooded with this kind of information.
Hope that helps, and maybe other people have different hints.