Not directly. You could imagine the ways that they could accomplish it thought by having someone on the outside do it for them.

The inmates can send all the letters they want, provided they buy stamps in the commissary for postage. The inmates without money on their books can get stamps and letter writing material for free (as indigent inmates).

It is a physical letter that is sent via USPS. The inmate gets to hold it in their hands. It is especially rewarding when they get pictures in that envelope at mail call, too

yes ma'am, unless the pictures show a little too much skin, they might get rejected. please keep em coming, we all appreciate it!

The inmate will know when they are at mail call that they have a letter from you. It is a physical letter that is actually handed to the inmate.

You can, however, the prison mailroom staff might not allow the inmate to receive it. The best way (by the rules) is to have it come in through Attorney Mail (legal mail). The staff cannot deny the inmate their legal documents. 

You cannot send stamps or other stationery to an inmate in a federal facility. These items must be bought at the commissary. Indigent inmates may receive these items at no charge, provided they have no money deposited into their trust account for a period of time.

You MUST affix a stamp to any letter being sent into a federal prison or any facility. None of them accept US Mail and pay the postage, you have to.

Usually within 2-3 days, provided that there are no hold-ups in the mailroom by the prison's staff

You can contact him by writing. Inmates cannot receive incoming calls