What is the IMEI of the BLU Life One X2?
It will work as it has the correct Bands for TMO but it does look like even though it has Band 12 BLU hasn't enabled the VoLTE and E911 on it so you wouldn't have access to TMO's extended LTE (Band 12 - 700 A Block) which helps in building coverage and fills in coverage gaps between towers.
Other LTE band 12 phones listed below are not compliant. Due to lack of VoLTE support you won't be able to place and receive calls including 911 calls in some buildings and some outdoor areas where 2G GSM and 3G HSPA+ signal (marketed by T-Mobile as "4G") is too weak or non-existent while LTE band 12 is available. You will still have data connection and you can receive and place non-emergency calls via Google Hangouts app (using Google Voice number). To place an emergency call you will have to either move outdoors where 2G or 3G signal is available or disable LTE to make your phone roam on another GSM network.
- Alcatel OneTouch Idol 3 5.5" 6045I and One Touch Idol 3 4.7" 6039S (more info)
- ASUS Zenfone 3 Deluxe ZS570KL (VoLTE confirmed not supported)
- BLU Dash X LTE, Dash X Plus LTE, Vivo XL, Life XL, Life One X, Studio Touch, Studio X Mini, Studio One, Studio Selfie LTE, Studio One Plus, Studio LTE 7.0, Life One X2
- Cat S40 and S60
- HTC One M9 Unlocked & Dev Edition (VoLTE confirmed not supported)
- Huawei SnapTo G620-A2, P8 lite ALE-L04
- LG G5 RS988 (VoLTE not supported)
- Microsoft Lumia 640 LTE Dual SIM RM-1075, Lumia 640 XL LTE Dual SIM RM-1065, Lumia 950 XL (VoLTE confirmed not working)
- Sonim XP7 Extreme
- Sony Xperia M4 Aqua E2306, Xperia C5 Ultra E5506, Xperia C4 E5306, Xperia Z3+ E6553 , Xperia Z5 E6603 , Xperia Z5 Compact E5803 , Xperia X F5121 and F5122, Xperia XA F3113, Xperia XA Ultra F3213, Xperia X Performance F8131 and F8132
- Verykool SL5000 Quantum, Fusion SL4500, Maverick SL5550
- ZTE Axon A1
Devices compatible with Extended Range LTE - Spectrum Gateway While not an official TMO site, it has proven to be pretty accurate. The above text is from their site and is near the bottom of the page.