Can I modify my magento to register with E-mail and ceellphone number?
With e-mail you not only can, but since it is you user id, you have to.
Phone is somewhat different thing altogether: phone number is not really part of user data -- it belongs to shipping or billing address object. Why it's there? Because you can order stuff to other people, as a gift or whatever. Another thing is that to encourage people to register only minimum amount of data is required up front: e-mail (user id), password and wether or not you want receive e-mails. Many people consider phone number a sensitive personal data and do not want to spill it up front which leaves considerable dent to number of guests conversion to registered users.
But if you still want to have a phone number as a part of core user data, there two options for you: one is to use Magento EE which has an option to add attributes to the user data. Another option is to use a custom extension to add attributes without EE. I'm sure couple of respected extension providers who frequent this forum will not leave the opportunity to strut their stuff unused
Pronto is right, you should add more fields to the registration form in case you absolutely need them.