Are UDID registrations real There are services like https://udidregistrations.com where you can register you UDID and get Certificates and Provision profiles. Are they worth? What danger is there? Signing applications is real?

Why I ask: I want to "play" a little with Xcode and Objective-C and have the possibility to test on my iPhone, but don't want to pay 100$ just for playing.
I am the administrator from UDIDRegistrations.com. I want to state that we do not support piracy in any way shape or form. Any members that promote piracy are immediately banned. 

We simply allow you to join our development team so you can sign your own developed applications and test them on your own iDevice. By extension of doing this, your iDevice is registered which will allow you to install betas granted you have downloaded the files yourself.

You can use Certificate &amp; Provisioning to develop with Xcode and test on your registered device. Obviously, it cannot be submitted to the App Store unless you have your own developer account. But paying a fraction of the fee to start developing is well worth it! 

Additionally you can use InstaSign and Zeusmos to sign these applications on the go.