I want a phone that tests network signal strength for each call-- and uses the best network each time. I might use Verizon in the morning, AT&T at noon, and Sp

I want a phone that tests network signal strength for each call-- and uses the best network each time. I might use Verizon in the morning, AT&T at noon, and Sprint in the afternoon, depending upon how many real bars the phone is getting. For each Latitude/Longitude the carriers should have a realtime +/- score of how well they support that area.