It would appear that LMY48I (which has a fix for Stagefright) is wreaking havoc on Nexus 6 phones with T-Mobile USA SIM cards. The phone simply refuses to connect to the cellular network, and thus calls and text messages are out the window. This issue seems to mainly be affecting people who upgraded from LYZ28E (T-Mobile USA's unique build with Wi-Fi calling) to LMY48I by flashing factory images. This likely has to do with the fact that the Wi-Fi calling-enabled radio firmware used in the LYZ28E build is quite a bit different than the "standard" radio firmware used in the more mainstream LMY47Z build.

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