What carrier does Helium Mobile use?

Could you please elaborate on the carrier that Helium Mobile utilizes for its services? I'm particularly interested in understanding the network infrastructure behind this innovative mobile provider, as it seems to be leveraging blockchain technology in a unique way. Are they partnering with established telecom companies, or have they developed their own proprietary network? And how does this choice of carrier impact the overall user experience and accessibility of Helium Mobile's services?