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A similar-but-different situation that we sometimes find in the UK is the presence of two lines and a neutral in the service cable to an older building. Because we've never used split phase 120-0-120V in the UK it is not common and usually indicates a legacy configuration, found in one of two kinds of locations.
One is where it was intentional; high load installations (e.g. farms) in rural areas where the only HV nearby was single-phase. For these, we supplied split phase 240-0-240 and ran large motors etc between the outers at 480V. It's the same deal as US 120-0-120 but twice the voltage, however we never added a high-leg to make it into a 3-phase service, i.e. it never formed part of an edge-grounded delta. Some of these installations still exist.
The other reason for two lines, found in towns, was a consequence of the switchover from DC to AC. Where the original distribution and service cables were laid for 3-wire DC, there were two outers and a neutral. Alternate houses would be supplied from the +ve outer and -ve outer, with larger installations receiving both outers to run motors, heating etc at 480V. When these areas were changed over to AC, a new 4-wire distribution cable was needed, but the existing service cables were often retained. 3-wire service cables were connected to two phases and neutral, resulting in 400V between the lines, not 480V. This is never supplied to a customer as a single supply, only as two separate single-phase supplies. I have this in my house, which has its original 1920s 3-wire DC service cable. As they are on different phases both lines can be fully loaded without overloading the neutral, so I can have 2 x 100A 230V supplies for a total of 46kW.
One is where it was intentional; high load installations (e.g. farms) in rural areas where the only HV nearby was single-phase. For these, we supplied split phase 240-0-240 and ran large motors etc between the outers at 480V. It's the same deal as US 120-0-120 but twice the voltage, however we never added a high-leg to make it into a 3-phase service, i.e. it never formed part of an edge-grounded delta. Some of these installations still exist.
The other reason for two lines, found in towns, was a consequence of the switchover from DC to AC. Where the original distribution and service cables were laid for 3-wire DC, there were two outers and a neutral. Alternate houses would be supplied from the +ve outer and -ve outer, with larger installations receiving both outers to run motors, heating etc at 480V. When these areas were changed over to AC, a new 4-wire distribution cable was needed, but the existing service cables were often retained. 3-wire service cables were connected to two phases and neutral, resulting in 400V between the lines, not 480V. This is never supplied to a customer as a single supply, only as two separate single-phase supplies. I have this in my house, which has its original 1920s 3-wire DC service cable. As they are on different phases both lines can be fully loaded without overloading the neutral, so I can have 2 x 100A 230V supplies for a total of 46kW.
