I think Tesla will still be losing money on this at $10/mo.
That's doubtful. A regular wireless provider has to account for a lot of expenses that Tesla can ignore (or consider a normal part of business):
By buying wholesale and doling it out to individual cars I expect it to be somewhere between revenue-neutral and slightly profitable. And it's something that Tesla is free to change the price on in the future.
Wall Street would normally go gaga over a company that had the kind of customer growth Tesla has when every customer has a Tesla account for recurring billing, a direct portal to their phone and a large touch-screen in their car that can be used as a point of sale terminal. Tesla is currently choosing to not monetize this in any significant manner at this point in time but I suspect it is what will drive revenues to be able to rapidly expand production capacity (batteries, cars, trucks and solar) and enter new markets in the future. The disruption that is upon us will be shocking in terms of how quickly things change. Having revenue levers that are easy to pull will be a key component in leading the disruption. Demand will be essentially unlimited so being able to quickly build new production and delivery facilities will be key.
I don't expect huge profits for years, I do expect unbelievably fast growth.