I have not upgraded to iOS 4. So, is it possible to sync iPhone Notes with GMail without iOS 4?
I don't think so, but a workaround is composing an email and saving it as a Gmail draft in the Mail app. Alternatively, you can use Evernote's iPhone app. If you own a Mac, MacWorld suggests "disguising your notes as something else. In Address Book, create a new contact and place your text in the contact’s Notes field. Mark it as a business and give it a useful name".