[multjoy]

Your VOIP number can be resolved to your mobile number. Your cell provider has the link.

You withholding your caller ID only hides it from the receiving handset, it doesn't disguise it from the network.

[getcrunk]

If you host your own pbx, you can consider it as a proxy to your cell phone, and even do it over vpn. You cant track that further than the pbx server ip