It turns out the budget shows the phone number registration problem: the costs to deal with phone number verification seem to be $6MM, which seems to be 10% of the entire budget.
If Signal staff are reading this, I'd gladly pay $100/year for a phone-free solution for all users.
You might understand that it's a bad idea, but that makes you an outlier.
Let one communicate from a computer (or phone) with a username+password account, with people who use the service with phone number account.
This without the mechanism Whatsapp uses, where you can use it in a web browser, but it's still linked to your phone.