NOTICE: This question falls into the FAQ page...
What type of questions can't be answered by Vocaloid Wiki
Questions on How to become (a part of the Vocaloid business / an official illustrator / a Voice provider for Vocaloid), and other similar questions.
As previous stated on the Main Page, the Vocaloid and Answer Wiki consist of contributors and fans, thus they have no inside knowledge on how to be a part of the business involving Vocaloid.Contributors are free to give their theories, but take caution of the information provided. See page history
Each studio has a set amount of plans for future Vocaloids. This does not mean it's impossible to become a provider, as some studios have now done contests to choose who becomes a provider.
If you are a native English speaker then chances are you are restricted to vocalisig a English Vocaloid. So far there has been no opportunity to be a provider for English Vocaloids. Before you get your hopes high, be aware that English takes a long time to do. Even if you ever become a provider you've got to sit through many hours of recording sounds in different keys. This will happen no matter what Vocaloid language you do and will take at least 4 hours (without any breaks) to do.
UTAU is a free alternative to Vocaloid and you can make your own UTAU with your voice for free.