T100 or T105

Try this, especially you use T105 with S*l Hi-card (> pre-paid card, as
Hi-card has longer wait between "calling" and "connecting" due to remaining
$ value announcement)

1. make a call to anyone
2. During display of "calling" (ie while $ value announcemnet)
3. adjust volume of speaker via side sliding switch
4. press NO as decided no to call

The phone will just display "calling" on screen and hung.
The phone will accept incoming call.
The phone will beep if sms come in but you cannot display the message.
Except YES/NO/C key, no other key cannot be used. You can only power off by
removing battery.

After you remove the battery to reset the hung condition. Some critical
setting is lost (eg, phone lock)

Firmware is at latest R9D. There is no fix to this problem currently.

This is a quick way to simulate hung problem. This phone currently can hung
without good reason. But above method will make you phone hung almost
everytime.