The SM-T211 is the 3G version. Ensure you have flashed a ROM specifically built for the T211, not the T210 (Wi-Fi only), or your cellular radio will not work.
The is a legacy device (2013) with a Broadcom SoC , not a Qualcomm or Exynos chip. This makes custom ROM development extremely difficult due to closed-source drivers. Unlike popular devices (e.g., Galaxy S2, Nexus 7), the SM-T211 has very limited custom ROM support . custom rom for samsung galaxy tab 3 sm-t211
But here is the good news:
If you don't need modern apps and just want a fast e-reader or MP3 player, this is the best custom ROM for the Samsung Galaxy Tab 3 SM-T211. It removes all Google bloat and Samsung spyware. Boot time is under 20 seconds. The SM-T211 is the 3G version