Sending variables

Hello
When using Isotope, in the checkout you can either log in or continue shopping without logging in.
In second scenario you have to put in your details like firstname lastname email etc.

Question is, where does Isotope puts those data? I would like to use them in a further step, for example for my summary or payment information. In another words - how can I put that data into php variables so I could use them later??

Thanks in advanced