@Wekkel: The SIM-in SIM-out method every 2 seconds described on pg. 16/17. Just make sure to disable PIN and use a non-T-Mobile SIM (including other companies using T-Mobile network; Vodafone worked just fine). Then, updated the FW without any SIM inside.
Note: It didn't work with a SIM with PIN...until I disabled the PIN.
Note: It didn't work with a SIM with PIN...until I disabled the PIN.