Spectrum Mobile, the mobile service available only to Spectrum home internet subscribers, finally has a Bring-Your-Own-Device (BYOD) option, but it's not true BYOD since it is currently limited to Apple and Samsung devices.
Spectrum Mobile launched in July 2018 but with only a limited selection of Samsung flagship phones that you had to buy from them. Then, in December 2018, Spectrum Mobile added iPhone support and now you can BYOD an Apple or Samsung device.
The service runs on the Verizon network, so potential BYOD customers should ensure their device is compatible with Verizon.
It's unknown when or if Spectrum will open BYOD to other Verizon-compatible devices.
Spectrum Mobile is a decent and inexpensive low-data option for those who already have their home internet service, with a 5GB cap on mobile hotspot data on the "unlimited" plan, or a pay-by-the-gig option.
For all the plan details and gotchas, please see our Gear Center entry for Spectrum Mobile.