You can't do that with FSX. Flash the phone with GENERIC firmware.

W810 CID 49:
Downloads - R4CE012_RED49 - W810_R4CE012_FS_S_E_EUROPE_RED49 - Top Sony Forums
Downloads - R4CE012_RED49 - W810_R4CE012_MAIN_GENERIC_HN_RED49 - Top Sony Forums

W810 CID 50:
Downloads - R4EA031_RED50 - W810_R4ED001_FS_S_E_EUROPE_RED50 - Top Sony Forums
Downloads - R4EA031_RED50 - W810_R4EA031_MAIN_GENERIC_HN_RED50 - Top Sony Forums

Custpack:
Downloads - w810custpack - W810_CDA102555_3_R2A_Generic_S_E_EUROPE - Top Sony Forums