The conventional Joomla registration forms includes a limited group of fields available. What is the "correct" way of adding anyone's name, surname, and telephone number towards the registration project? I'm able to certainly customize the Joomla core, but that is under ideal.

A nickel for the ideas.

Basically, you will need to code options for com_user and mod_login, then store your extra information inside a separate table, keyed by user_id. Community Builder does such like, only on the much bigger scale. Could also be other similar profile extensions that behave as drop-in options towards the core login system.

The easiest method to get it done (and many consistent with Joomla 1.6 - when it is launched) is by using the Joomla User Meta wordpress plugin. UserMeta

You are able to extend the profile with the user xml file but this will not store these questions database, basically as parameters. The Usermeta is a lot more robust.

I accomplished this using the CBE extension for Joomla! Based on your requirements that could be overkill for you personally, but when you'll need profile management with avatars along with other features you can look at going that route.