A writer with work and personal lines on one Samsung phone cut SIM prompts from about 35 to 3 in five days with two settings Samsung barely points out.
Samsung phones with two SIM cards can stop asking which line to use before every call. A writer at Android Police tracked five days of SIM choices, then changed two settings and repeated the routine. Prompts fell from about 35 to three. The settings are easy to miss, and one has a gap that matters for prepaid plans.
The writer keeps a work line and a personal line on one Samsung phone. Samsung's SIM manager offers two choices for calls: set one SIM as the default, or have the phone ask each time. A single default would mix work and personal calls, so the phone was set to ask. Over five days, the writer picked a SIM about 35 times and used the wrong one at least seven times, which meant explaining who was calling.
Texts were easier because Google Messages remembers the SIM for each conversation. Switching during a network problem was slower, though. In February 2025, a Messages update moved the one-tap SIM switcher into each conversation's details page.
The first setting lives in the Contacts app, not the SIM manager. Open a contact, tap Edit, and pick a preferred SIM for calls. The second is auto data switching. Both have been on Samsung phones since its Android 12 update, but nothing on screen points to them.
With both settings on, the phone prompted only three times, all for numbers rarely called. The writer set a preferred SIM for each right after the call. Switching SIMs for texts dropped to zero, even though the network went down a couple of times. Samsung says the feature keeps calls and texts working on a SIM with no coverage by routing them over the other SIM's mobile data. Work messages kept going out from the work line.
There is a limit. This only works for VoLTE calls, which run over the 4G data network, and RCS messages, a newer kind of text.
Auto data switching follows coverage, not data balance. A SIM with a strong signal and an empty data plan still looks healthy to the phone, so it stays on that line. The writer still had to switch the data SIM by hand in that case. Anyone on a prepaid plan that runs out of data should expect the same.
Other phone makers handle this differently. Google's Phone app on Pixels has a Set calling SIM option inside each contact. Motorola's Smart SIM makes a SIM the default for a contact after three uses. The writer argues Samsung should offer the per-contact choice during setup. Android still treats one SIM as primary and the other as backup, and the writer is getting a second phone.
On a dual-SIM Samsung, set a preferred SIM per contact in Contacts and turn on auto data switching, but switch data by hand if a plan runs dry.
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