I have straight talk on my nexus 5 android 5.1.1 and I'm using the AT&T Sim from the BYOP kit. I'm just having data/internet issues. The phone shows almost full bars with the LTE symbol but won't connect to the internet. Sometimes after timing out several times it will reconnect to hspa and the internet works fine under hspa/3g until reconnecting to lte. Or sometimes it shows that it is connected to LTE or hspa and just no actual connectivity until forcing some type of reconnect via reboot or toggle options. I've tried several different APN settings nothing seems to work.