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Companion app

Plain SMS works over ADB alone, but picture messages (MMS) and group threads need a small helper app installed on the phone. dumbsms installs and manages it for you from Settings.

What it does

The companion app runs on the flip phone and handles the parts ADB can't do cleanly on its own:

  • Sending and receiving picture messages (MMS)
  • True multi-recipient group threads
  • Pulling inbound MMS image bytes (blocked over raw ADB without root)
  • Near-real-time notification when new messages arrive

Without it, dumbsms falls back to adb-fallback mode — plain SMS only. You'll see that called out in Settings next to the connection mode.

Install from the app

With the phone connected over USB and developer mode enabled:

  1. Open the Settings gear in dumbsms.
  2. Find the companion app card.
  3. Click install companion.
  4. Wait for status to show installed and capabilities to list SMS/MMS features.

If a newer version ships with your dumbsms build, the button reads upgrade instead of reinstall. Use reinstall to repair a broken install.

TCL Flip Go — special case

4058W · one whitelisted sideload slot

T-Mobile's retail firmware on the TCL Flip Go actively blocks sideloading. It isn't a storage problem — the phone lies with INSTALL_FAILED_INSUFFICIENT_STORAGE when the real issue is an OEM gate. Two things have to be true before any APK can install:

  1. The package name must be com.debug.loggerui — the only id on a hardcoded whitelist (dumbsms wears this disguise on purpose).
  2. An OEM flag install_enable must be set to allow installs (dumbsms handles this automatically during install).

You don't need to run any of this by hand — the install button in Settings does it all. But if you're curious about the reverse-engineering rabbit hole, read The one app this phone will install.

The TCL is also the slower dumbsms phone — roughly 10× the Sonim moving data, especially over Bluetooth (~1.2 K/s vs ~15 K/s). Companion installs and MMS byte pulls over BLE can feel sluggish; USB is faster, but still behind the Sonim.

Sonim XP3plus

The Sonim doesn't have the TCL whitelist gate. The companion app still unlocks MMS and groups, but install should be straightforward once developer mode and USB debugging are on.

Verify it's working

In Settings → companion app, check:

  • status: installed (not "not installed" or "upgrade available")
  • capabilities: lists MMS-related features
  • missing perms: should be empty — if not, try reinstall

In Settings → phone, the connection mode should not say adb-fallback, MMS not supported.