Yesterday, Apple unveiled its Series 3 Watch, which will have cellular LTE capability. The question many had, though, was about the cost. Not of the watch itself (the cellular version starts at $399), but how much on top of that will you have to pay your carrier to use it? Now, we can give you a number. An Apple Watch Series 3 will cost you $10 per month on your cell plan, and it appears that all US carriers will offer three months of free service (a $30 credit). However, we're still waiting for confirmation from Sprint.