Much like a traditional phone, anyone that has your registered Tango phone number will be able to add you to their address book and call you on Tango. This is also true for your registered Tango email address. Removing your email from your Tango profile will only allow people who have your phone number to see you in Tango.
Other Tango users that you've sent and received a chat message with will also be able to call you.
If you want to disable the ability for someone to call you, you can use the Block option.