It's not about carriers. It's about delivery logistics and warranty coverage, as well as about compliance with local regulations (FCC and etc.). They can do all that without dealing with carriers. One doesn't need to care about juggernauts. Just offer an option to buy unlocked handsets in each market either through Jolla's official store, or through retailers but with normal warranty. That's it. Forget about carriers - there are more and more contract free / prepaid options emerging, which can be used with any decent unlocked GSM/LTE handset (just take care to cover all common frequencies - and you are set).