Voice banking is the recording of one's natural voice for the possible eventuality of losing one's voice. Services exist which will convert these recordings into a synthesised version of your voice which is compatible with Windows SAPI TTS (text-to-speech). Software which is also compatible with Windows SAPI TTS (such as Optikey) can then use your synthesised voice when generating speech. In short, if you bank your voice into a synthesised version you will be able to use it with Optikey and other speech generating software should it become weak or lost entirely.
Multiple services exist, but ModelTalker.org currently offers this service for
free $100. The general process involves obtaining a suitable microphone or headset and recording 10 trial sentences. These are uploaded to ModelTalker who will evaluate the recordings and give you feedback on whether you are ok to continue, or if you need to make adjustments to improve the sound quality. The next stage involves recording 1600 phrases, which you can split into as many sessions as required (if your voice is weak try recording first thing in the morning and stop when you feel tired). Finally your recordings are uploaded and a synthesised version of your voice is created and made available to you. All that's left is to download it, install it and (if you want to use it with Optikey) select your new voice from the management console (in the "Sounds" tab).
More information on voice banking in general is available here.
N.B. I am not affiliated with the ModelTalker service and cannot offer any support for the voice banking process. I have included this information only because I have some first hand experience with this process and the results and (although voice banking may not work for everyone) I think this is an excellent service.
Tangentially related to banking your voice for your own use is the idea of recording messages for your loved ones. Inspired by this article on the BBC News website here is a link to the project where you can download the app and receive support. I think this is a great idea: RecordMeNow.org