Can I use a existing phone with the home phone sim or do I need to use the Hub?
You need to plug your home phone into the hub. There's room to connect 2 telephones to the hub but the best option is to use a cordless set with multiple handsets that way you connect 1 phone to the hub and plug the other phones in around the home where they are convenient as the hub needs to be placed in whatever location gets the best service (the most bars). The hub only needs to be connected to a power outlet to function unlike a regular landline service where you needed a phone jack to be located in a convenient location. Makes it way easier to find a good place to keep the hub and phone out of the way :D