Why not just make one up? You might need to use part of your real number to make it match other parts of your contact info to get past their filters.
For example:
In the U.S., phone numbers are organized as follows: 1-three digit area code-three digit prefix-four digits. Often, a website will require the area code and prefix to match the address and/or ZIP code (postal code). I give out fake phone numbers by giving my actual area code and prefix followed by four random digits. Works every time.
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Autism Speaks does not speak for me. I am appalled to discover that Alex Plank has allied himself with an organization that is dedicated to eliminating autistic people. I no longer wish to have anything to do with Wrong Planet. Delete this account.