You can order complete device and have no trouble at all.
But if you want to buy just a board, then no soldering will be required. You just disassemble the device, put the N900 board aside and assemble it back with new board inside. It will provide its own new SIM housing. No soldering required. You'll just need a small manual rework to the case in order to fit MicroAB USB socket into the hole made originally for MicroB.