iphone 5

My iPhone 5 gets very poor reception in Milpitas, nearby to McCarthy and Montague no matter where I am inside our building. Outside I only get 3 bars.. I was using a 3G iPhone on ATT but switched from ATT to Verizon because there is a Verizon antenna on the roof of our 2 story building. My reception is worse.

My friend uses a Samsung with T-Mobile and gets good reception.

It seems like the iPhone 5 has a weak signal amplifier (antenna).

What can I do?