Yes, SMS is store and forward. Charging happens immediately when the message is sent. They don't care what happens after that. (This has been discussed especially for premium SMS services. If the user mispells the search, order or what ever service she was trying to use, she well end up paying for service that was never fulfilled.)
We have 5 mobile subscriptions in the family. Only one "won in the lottery" Of course I cannot be 100% sure that the number came from my Google account creation, but it was definitely the closest use of this phone in relation to spam. As I wrote the subscription is very much unused. Not saying that Google themselves do it, but certainly they are interesting for spammers.