If the Sony Ericsson Xperia X10 unable to detect, read or if the phone does not recognize the SIM card. It could be the SIM card that is damaged or it could be a phone problem?
Here's the solution on how to fix the problem....
Try to insert a different SIM card on the phone and check if this works. If it does not work, visually check the SIM card connector for possible damaged or clean it if necessary.
Try to repair the device firmware using PC Companion. If it still does not work, the problem may possibly on the phone's hardware components.
The solution below shows the connection line paths and components that holds of the Xperia X10 SIM card circuit. This may help in troubleshooting sim card problem issues.
On Sony Ericsson Xperia X10 the Sim card connector or slot is mounted on flex board assembly together with the microSD memory card holder. If the said flex is damaged it may result to "sim card and memory card not recognized problem". The the whole Sim card flex board is replaceable and it's not hard enough to find or purchase a replacement for it.
VSIM or VUIM, RESET, CLOCK, DATA and GROUND connections.