Possible to dynamically change phone number on landing page?

There is a HTML5 geolocation api but I think the rules indicate that the user must agree to be geolocated.  So not sure if there is a dependable way of gathering their location information

Have you tried creating a segmenation based off the inferred locations? (Inferred City, Inferred State Region, Inferred Postal Code...)
They are populated for alot of anonymous leads too and there is a whole bunch of them to select from. And then set your 800 number as default for those few anonymous leads that don't have it populated yet.

I have the best luck with inferred State and Country.
 

I'd use a Segmentation & Dynamic Content/Dynamic Snippet.

If you passed the user's location as a parameter in the landing page URL (landingpage.com/?location=california), then you can set up custom JavaScript to change the phone number. This StackOverflow post describes how to get value of a query parameter.

I think this is a good topic for the Marketo Developer Blog. I'll work on creating an example. 

 

Thanks for the suggestion. I had not thought that this would work with anonymous leads. It seems a bit temperamental? See my unsubscribe confirmation page here (http://pages.crfhealth.com/Unsubscribe---Confirmation.html) - there should be a tele number to the left of the email address in the footer. For me, an anonymous lead, it works on certain pages and not others. Any ideas here why it isn't defaulting properly? I've checked the preview and it works well when using the previewer. 

Works in IE but not Chrome. Very weird. Could be privacy settings or something? I'd imagine the DEFAULT snippet would show up regardless.