Sim card not accepted - Cell Phones

It depends on the kind of sim card you a re inserting, First, the sim card may be damaged, or probably the sim port on the phone may be damaged or bad. Then secondly, not all sim work with all phones, like the CDMA sim only work with cdma phone and it won't work on any other phone except cdma phones and normal mobile sim will not work on a cdma phones as well. verify all this to know where the problem comes from...if probably you try another sim on the and it works, it means that the sim card is the problem but if it doesn't work then the problem is directly from the phone, i.e. the sim port on the phone, you can then take your phone to an engineer for repair or the customer service center for repair. Thanks