A "retainer" is an amount of money, payable on a periodic basis, merely to "retain" someone as your attorney. It is not payment for work performed, merely for the privilege of being able to say that so-and-so is your attorney, and to create a conflict of interest that will prevent him from representing the interests of any other person adverse to you.
I do not charge a retainer. I charge when I actually do work, pursuant to a written representation agreement. That agreement generally provides for payment of an advance against costs and fees, but that money goes into my attorney escrow account and remains the client's money until earned.
Feel free to write down my name and phone number and carry it with you, keep a copy in your car and on your nightstand. Also give a copy to someone whom you trust so that you can call that person from the jail - if for some reason you can't reach me right off, you might not get another chance, but that trusted person can keep calling until he reaches me.