How long does a Subscription ID stick around in Android?

Question

Starting on API Level 22, there is native support in Android for Dual-SIM devices. At the center of the APIs, there is SubscriptionInfo.getSubscriptionId().

Using these IDs, you can retrieve SmsManagers for each respective SIM card to send SMS and MMS. You can also identify through which SIM card an SMS was received on the SMS_RECEIVED_ACTION, and so on.

However, what is the lifetime of a Subscription ID? Can I store a Subscription ID in a local database and count on it to still be valid and pointing to the same SIM card later? By later, I mean after rebooting the device, removing its SIM card and popping it back in, or even after factory resetting the device.

Answer 1

I tested the resilience of SubscriptionId myself, using two SIM cards, though on a Single-SIM device, since that is what I had available at the time.

First, I noted the SubscriptionId the system was giving me when SIM Card A was inserted. The SubscriptionId I was getting had a value of 2.

Next, I restarted the device. The SubscriptionId after restart was still 2.

Then, I turned off the device, removed SIM Card A and put in SIM Card B. After turning the device back on, the SubscriptionId changed to 4.

Lastly, I turned the device back off, removed SIM Card B and put SIM Card A back in. After turning the device back on, the SubscriptionId changed back to 2.

In conclusion, it looks like Android assigns a SubscriptionId unique to each SIM Card. The SubscriptionId seems to survive system reboots, and SIM Card removal and reinsertion. I did not test factory resets, but my gut feeling is that it probably will not survive those, since the system would not have any history of interaction with a SIM Card after a factory reset.