Just saw this log when the baseband crashes.
It happens a minute or two after going into sleep mode.
See this thread for more info about this problem: http://www.hackint0sh.org/forum/showthread.php?t=7699

Reason: modem reset
Date: 10/8/2007 18:39:37
IMEI: xxxxxxxxxxxxxxxxxxxxxx
OS-Version: 1C28
Firmware-Version: 03.14.08_G
Uptime: 28

SC response (0 bytes).
14256971 reg: Entered low power at 18:18:16 (+120) 10/08/2007 ST (12282)
14257185 ipc: *** Baseband crash detected! ***
14257185 rm: reset called with reason modem reset
14257185 rm: Reset: modem reset
14257225 rm: ENTER: resetCommon
14257225 rm: start reset dispatcher state
14257225 rm: end reset dispatcher state
14257225 evt: Sending internal notification kEventRadioOff (6) params={0, 0, 0x0}
14257226 clm: Clearing DTMF queue
14257226 evt: Sending event kOperatorNameNotification (14)
14257226 evt: Sending event kServiceProviderNameNotification (13)
14257226 evt: Sending event kRegistrationStatusNotification (11)
14257226 evt: Sending event kDataAttachStatusNotification (110)
14257226 evt: Sending event kRegistrationStatusNotification (11)
14257226 evt: Sending internal notification kEventNotRegistered (3) params={0, 0, 0x0}
14257227 evt: Sending event kSimToolkitMenuNotification (97)
14257227 evt: Sending event kSimToolkitSetUpIdleModeTextNotification (105)
14257227 evt: Sending event kSimStatusChanged (138)
14257227 rm: start reset dispatcher state
14257227 rm: end reset dispatcher state
14257302 rm: exit low power

I'll post the full log later on.

Anyone understands or has some speculations on whats going on?

Where can i check the log? I want to see if mine is similar. My phone also dies after going to sleep.