2. Smudges / dirt on SIM
Smudges and dirt are both a popular cause for the SIM card error. If the SIM you are inserting in your iPhone 4 has any traces of dirt or smudges, rub it with a slightly damp cloth, then wipe with a dry cloth, and make sure that the SIM has been properly cleaned and dried.
3. SIM not properly inserted
If the SIM is not fully or properly inserted, then you can get the no SIM card error. Try wiggling the SIM a bit, insert it fully in the SIM tray, and then check again. You may also insert a tiny piece of paper between the SIM and the SIM tray, to ensure that it is not too loose in the tray. Alternatively, you can put a piece of masking tape on the back of the SIM so that it can properly fit in the SIM card tray.
4. SIM card size
Apple iPhone 4 uses a Micro SIM that measures 15 mm × 12 mm while the standard SIM measures 25 mm × 15 mm in size. The metallic part of both the SIM’s is the same, just the total size of the Micro SIM is smaller. This size difference can also cause the no SIM card issue to occur. So, you can cut your standard size SIM to make it a Micro SIM. To do this, you can use a butcher knife, but the better way to do this is to use a SIM cutter. You can buy a SIM cutter from your local phone store or buy it online from Amazon, at $ 7.95.
There are also some other possible fixes besides the above four. These fixes will resolve the problem only temporarily – for a few minutes or a few hours maybe. But, if you and your iPhone 4 are lucky, maybe these fixes permanently resolve the no SIM card issue. So you can give them a try as well:
a. Turn off the iPhone
Turn off your iPhone 4, wait a few minutes and then turn it back on.
b. Airplane mode
Turn on Airplane mode, wait a few seconds and turn Airplane mode off. This can also resolve the problem.
The above fixes will resolve the no SIM error iPhone 4 issue. But, if none of the above fixes work, no other fix will work either. So just go to the Apple store, and have your iPhone 4 replaced with a new one.
Image Credit: blog.daveburrows.com