[HTC Desire S] Jann F:
I don't really know, it depends on what hboot you are...

My ENG 2.00.2002 hboot just echo's [ERR] Command error !!!

Somebody with a relocked hboot should try it ;)

EDIT: Oh and be careful with the TASK command!!! There are tasks that just wipe the whole phone ;)

EDIT1:

Oh and here a list of all commands, extracted by me via fastboot oem h^^

(bootloader) command list
(bootloader) mb
(bootloader) mh
(bootloader) mw
(bootloader) ew
(bootloader) eh
(bootloader) eb
(bootloader) mmu
(bootloader) ram_test
(bootloader) jump
(bootloader) test
(bootloader) sdtest
(bootloader) eraseconfig
(bootloader) writeconfig
(bootloader) readconfig
(bootloader) writesku
(bootloader) readsku
(bootloader) rflash
(bootloader) tflash
(bootloader) block_test
(bootloader) partition_test
(bootloader) rbchk
(bootloader) erasesd
(bootloader) btrouter
(bootloader) tick
(bootloader) heaptable
(bootloader) emapi
(bootloader) emapiTest
(bootloader) emapiCountryID
(bootloader) emapiWlanMac
(bootloader) emapiSetDefCal
(bootloader) emapiReadCal
(bootloader) lr
(bootloader) imgcrc
(bootloader) resetautoimage
(bootloader) resetpreferdiag
(bootloader) resetRUUflag
(bootloader) writeserialno
(bootloader) readserialno
(bootloader) battcheck
(bootloader) enter
(bootloader) gotofastboot
(bootloader) gotohboot
(bootloader) writemid
(bootloader) usbtestmode
(bootloader) eraseWifiFlash
(bootloader) erase
(bootloader) readmbserialno
(bootloader) listpartition
(bootloader) erasebcid
(bootloader) writebcid
(bootloader) readbcid
(bootloader) fmrouter
(bootloader) fmtx
(bootloader) resetuP
(bootloader) bdaddress
(bootloader) wMfgTp
(bootloader) rMfgTp
(bootloader) emptypagecheck
(bootloader) saveprt2sd
(bootloader) savemem2sd
(bootloader) savefb2sd
(bootloader) emapiInit
(bootloader) emapiChannel
(bootloader) emapiBand
(bootloader) emapiRate
(bootloader) emapiRateset
(bootloader) emapiCountry
(bootloader) emapiTXpwr1
(bootloader) emapiPkteng_start
(bootloader) emapiPkteng_stop
(bootloader) emapiOut
(bootloader) emapiFqacurcy
(bootloader) emapiCrsuprs
(bootloader) emapiUp
(bootloader) emapiDown
(bootloader) emapiMpc
(bootloader) emapiCounters
(bootloader) emapiVersion
(bootloader) emapiEtheraddr
(bootloader) emapinRate
(bootloader) emapiSetIrqPin
(bootloader) bkflash2emmc
(bootloader) fl
(bootloader) loaddiag
(bootloader) lnb
(bootloader) init_a1026_fw
(bootloader) checkKeyCard
(bootloader) usbspeed
(bootloader) ats
(bootloader) gpiow
(bootloader) gpior
(bootloader) mddiw
(bootloader) mddir
(bootloader) clock
(bootloader) i2cr
(bootloader) i2cw
(bootloader) i2ctest
(bootloader) ulpi
(bootloader) changeCid
(bootloader) read_l2_acc_fuse
(bootloader) qupi2cr
(bootloader) qupi2cw
(bootloader) pmgpiow
(bootloader) pmgpior
(bootloader) dgtest
(bootloader) entpa2051
(bootloader) bumpclk
(bootloader) switch_ddrfeq
(bootloader) ntrigsetcal
(bootloader) ltetest
(bootloader) sdio_loopback
(bootloader) sdio_setsize
(bootloader) sdio_readblk
(bootloader) sdio_writeblk
(bootloader) sdio_readblk
(bootloader) sdio_dumpreg
(bootloader) emmc_boot
(bootloader) fdisk_emmc
(bootloader) set_partition_emmc
(bootloader) erase_emmc
(bootloader) test_emmc
(bootloader) sector_erase_emmc
(bootloader) fat_format_emmc
(bootloader) init_emmc
(bootloader) reinit_emmc
(bootloader) write_mmc
(bootloader) set_wp_emmc
(bootloader) write_prot_test
(bootloader) clear_wp_emmc
(bootloader) set_enh_area_emmc
(bootloader) get_identifier_token
(bootloader) keytest
(bootloader) heap
(bootloader) boot
(bootloader) reset
(bootloader) powerdown
(bootloader) rebootRUU
(bootloader) heap_test
(bootloader) rtask
(bootloader) task
(bootloader) enableqxdm
(bootloader) gencheckpt
(bootloader) lock
(bootloader) list_partition_emmc
(bootloader) load_emmc
(bootloader) check_emmc
(bootloader) check_emmc_mid
(bootloader) read_mmc
(bootloader) get_wp_info_emmc
(bootloader) send_wp_info_emmc
(bootloader) get_ext_csd_emmc
(bootloader) get_sector_info_emmc
OKAY [ 0.152s]
finished. total time: 0.152s

as always, please be careful with those :)

//will move those into a thread in the dev area, some things seem interesting :D