如今，尤其是在中国，双卡双待如此普及和如此广泛，双卡双待已经成为智能手机的事实上的标准。大势所趋，为此，Android从Android 5.1开始，从Android SDK API层面开始支持双卡双待或1个以上的SIM卡。Android官方的文档阐释链接：
https://developer.android.com/about/versions/android-5.1.html#multisim
原文：
Multiple SIM Card Support
Android 5.1 adds support for using more than one cellular carrier SIM card at a time. This feature lets users activate and use additional SIMs on devices that have two or more SIM card slots.
You can access information about the currently active SIM through theSubscriptionManager
class, including whether or not the device is considered to be roaming on the current network. This information is useful for developers who want to throttle their apps‘ data access down or off for device users who are sensitive to data access charges. Your
app can be alerted to changes in a device‘s current network connection by requesting the
READ_PHONE_STATE permission and settingSubscriptionManager.OnSubscriptionsChangedListener
on theSubscriptionManager object.