Unfortunately we don't offer a domain registration or domain transfer / migration services. We did up until some dickwads decided to register domains via us and request refunds via Paypal. In effect they was fraud orders, Paypal would grant the refunds however we lost out.
The downside is, it's too risky and costly to offer that service. We will review this at a later date.
Hope that answers your question.
You can use your own domains registered elsewhere, you can simply use the domains and dns features in cPanel.