If your software is popular, it will attract motivated pirates.
First question, can you be more precise about your target audience and what your software does? Is there any incentive to copy it? Do you want to protect from customers buying less licenses than they really need?
In other words: what's your "threat".
Another question is: how do you license your software? Do you give a serial file? Serial number? Is it available for download?
As for 3rd party protection system, .NET applications are extremely easy to hack because you can almost decompile them. You'll find obfuscators and the like, but don't rely too much on them.
Phone activation will make you lose sales. Don't annoy your customers. Just make it clear what they can do and what they can't do.
Online activation will need work on your part even with a 3rd party module as you will have to build the bridge between your application and the protection.