I will have one cellular line, but it will service two lines. This will be SIM-1, and SIM-2. The price of service is affordable, and I can customize the plan to have just the features I need with each line. I will have 2 SIMs. SIM-1 will have 5GB of data, while SIM-2 will have no data added. This is fine as SIM-2 will just use the data from SIM-1. Both lines offers unlimited voice, and SMS. I would wish there was a way I could have a single voicemail box, but I will have to accept the fact that I would have 2 voicemails (1 for each number).
Since the phone lines will use my iPhone, both SIMs will be on the iPhone. This is why SIM-2 does not need a data service connection. Since both lines will be on an iPhone, there will be support for iMessage. In addition, the carrier supports RCS on iPhones which is important for me since I know a couple of people that prefer to use RCS.