What happens if u ignore a federal agents phone call?

Let's make this simple and straightforward. The police (including federal agents) are not your friends. If you value your freedom, then do not speak to any federal agent or police officer without your attorney present. Ignore this advice at your peril. Good luck.

They will probably make additional attempts to contact you. I don't know the details of your situation, but you should really think twice about helping them set somebody up to confess. They are not your friends and are obviously attempting to build a criminal case. You would be mistaken to believe you are immune from becoming part of the criminal investigation. You should consult with a local criminal attorney for advice before speaking to them.

While you haven't yet revealed the circumstances of the December encounter with Federal agents, and I strongly urge not to do so here, my best guess is that they have told you that they have something that they could charge you with. They gave you a "golden opportunity" to "help yourself." DO NOT BE FOOLED any longer. It is an opportunity for them, not you. It sounds like you've made mistake Number 1, don't engage in a second mistake by speaking with them any further until you have consulted with qualified criminal defense counsel first. Put them off anyway you have to--delay until you are protected by counsel. Most of us who participate here will provide you with an initial consultation without charge to you. The next step is really obvious. Good luck.