Google has now said that its revolutionary WiFi First mobile services in the US is not just for smartphones. Fi customers will be able to add up to nine devices, including iPads, using free data-only SIMs, as Google continues to disrupt the US mobile model. Remember Google Fi is a combination MVNO across either T-Mobile or Sprint, plus WiFi. Using a free data-only SIM card ordered from their Project Fi online account page, customers can access cellular networks at a flat rate of $10 per gigabyte. The option is only available, for now at least, to those who already subscribe to the main Fi service, which charges $20 a month for unlimited domestic talk and text, unlimited international texts, WiFi…