>> In theory there might be more than one IMS APN for a operator,
>> but I really don't see this as a real life scenario for this.
>> If anyone disagrees please speak out and explain...

One such scenario is the in-vehicle use model, where the ISP provides network connectivity via one APN and the auto manufacturer has network connectivity through a separate, private, and independent APN. Connectivity, billing, bandwidth, reliability, roaming etc are all independent for each network. For example, auto manufacturer X may contract with ISP Y for remote access to the car, while the owner of the car may prefer ISP Z for personal use.