I've looked everywhere online, I even called Sonim and asked them directly. Still can't come up with a pinout for the 3.5mm 4 pin to USB-A wire.
It's similar to this one listed, but I have no idea if it uses a standard or is custom.
I have a Sonim XP1520 on hand & just tested the pinout with a multi-meter.
The Sonim XP1520 & XP3400 use the same charger. So I assume the XP3410 would be the same as well. But you may want to double check that with Sonim.
Anyways the pinout for the XP1520 is:
Tip (1): Data +
Ring (2): Data -
Ring (3): GND
Sleeve (4): VCC
Similar to an iPod Shuffle cable but with the data lines flipped.