Depending on your setup... If I follow you, you're saying you have a phase 3 dish with 3 lnb heads. The dish has a built in 4-port switch to allow 4 active lines. If you have only the one receiver in the house, you are ok. If you have another DVR and a standard box, or 3 additional standard boxes, you will need to have a Multiswitch installed so that you can go beyond the dish's built in 4 available ports since each DVR requires 2 lines to be able to record 2 shows, or watch 1 live show and record another.
Long story short... unless you are going to HD, no new dish required, just possibly another device.