Doing so would make the plate dishwasher-safe, and the couple can also enjoy food in it. The plate may also be placed on the fireplace mantle, or shelf with a plate stand.
The invitees have the choice of noting down some marriage advice, words of wisdom, and best wishes for the newlyweds on these cards. After the wedding, a souvenir box can be bought to store all the cards. The box can be a plain white photo storage box embellished with extra tulle or ribbons, which were left after the decorations.
For invitees to write on the frame, a table would be required to be placed in order to hold the photo frame. The invitees can be directed to write on the frame, and informed that the newlyweds would be using it as a marriage souvenir.
The end result of this would be a soft-copy of the messages and best wishes, which can be saved onto a hard disk or any other portable storage device. Later, if you wish, you can incorporate the messages with any wedding snaps in a manner you desire. This is probably the best, advanced way to keep these messages alive forever.
These are just a few ideas which can be used to make your wedding a memorable and unique event. However, if you want to use your creativity, and make you own guest books, you are always welcome!