From the official android blog, The announcement post that today they will be rolling out an Android 5.1 Lollipop. The update is aimed at improving stability and performance and offer a few new features like support for multiple SIM cards, Device Protection and high definition (HD) voice on compatible phones.
With this kind of update all android lovers with Android 5.0 Lollipop dual sim will be able to use both the sims in the 5.1 Lollipo update. Android Lollipop 5.1 now lets you use more than one SIM card on a device with multiple SIM slots.
High Definition Voice Calling
Table of Contents for Unwrapping a new Android 5.1 Lollipop update
High Definition voice calling is now on your mobile phone. Get crystal clear calling with HD Voice between compatible Android 5.1 devices like the Nexus 6 on T-Mobile or Verizon.
With Device Protection, your lost or stolen device will remain locked until you sign in with your Google account – even if someone resets your device to factory settings. This feature will be available on most Android phones and tablets shipped with Android 5.1 in addition to Nexus 6 and Nexus 9.
Android 5.1 Lollipop also provides enhancements such as the ability to join Wi-Fi networks and control of your paired Bluetooth devices directly from Quick Settings.
Source: Official Android Blog