Step 1: Unassemble the Phone
Disassembling is not an easy task with this type of phone. You have to find these small plastic "noses" on the left and right side. Best I did to open the case was to slib between the small crack using my fingernails ... some broke during this. But finally the case was open and the parts lay in front of me.
Step 2: Putting Power on the Device
The red and the black cable are the ones that gat the power. The usb port is capable of giving you 5V on 1/2 amperes. This is enough for the phone to operate. Feed the cable through the hole in the plastic cover and solder it to the old battery contacts.
Step 3: Attaching the Power Switch
Step 4: Software
I wrote a simple script (hw-check.pl) to check the temperature of the cpu and the mother board. When one of the parameters goes to ALARM state a sms message is send to my mobile phone.
The sensors package is used to fetch the temperatures. In the tar file you can find a file (sensors-test.txt) that contains the sensor values that I read from my server.
Many of the sensors on the it87-i2c-1-2d adapter seems to be not connected. The voltage values may be useful but I think they are not worth an sms ;-)
I decided to ignore this sensor chip.
The lm90-i2c-1-4c chip shows values that seem to be useful.
I added a picture that shows a temperature alarm that the system generated. I send and received it on the same mobile device.