You will need to submit an MV2428, Personalized License plate application (regardless of the type of plate you will want later), and $15. You will receive confirmation via email or mail notifying you that the message is reserved for 2 years. This process cannot be done online or over the phone and must be mailed in.
When you want to order the physical plate, you will need to submit the reservation slip with the appropriate special plate application (based on the plate type that you want). If you do not request the physical plate within the 2 year time frame, you will need to re-reserve the message to retain it for another 2 years.