Most of the XBAND registers are at bank $FB.
$FB:C108 - Related to XBAND Cards. (Bit 0 is a XBAND Card Check)
$FB:C188 - ???
$FB:C192 - ???
$FB:C196 - Related to Dial-up. Must be #$80.
$FB:C1B0 - ???
$FB:C1B2 - Must be #$46 for running XBAND.
$FB:C1BA - ???
$FB:C1BC - Must be #$08 for running XBAND.
$FB:C1BE - ???