I'm redoing an existing shop in Magento, the client is requesting that when customers register, their customer number gets set to their mobile number (which is required, and asked for at registration). Now I personally don't think this is good practice, but it's something they're set on having. I'm looking into a proper way to do this. I am not quite sure what to override or where to start, as I've never altered registration before.
Is this possible? And if so, could you help point me in the right direction on how to accomplish this.