A variety of causes can lie at the heart of your Nokia E71's failure to connect to its Subscriber Identity Module card, most of which can be easily rectified. SIM cards are needed by Global System for Mobile Communications, better known as GSM, phones to gain access to these types of networks.
Card Condition
Your Nokia E71's SIM card can become damaged or corroded over time, especially if it has been transferred between devices extensively. SIM cards contain a highly-sensitive microchip that, if damaged, will cause the phone to fail to access the phone's processor. Connecting to the device's processor is how the information that is needed to connect to the provider's network is generated and prepared for transmission. If you suspect it has been damaged, replacing the SIM card is the only way to reestablish the connection between the E71 and its SIM card.
Installation
Installing the Nokia E71's SIM card incorrectly can also cause the phone to fail while attempting to access the card. Frequently, mobile phone users insert the SIM card upside down or backwards, which can cause damage to the card or can make the card inaccessible to the phone. The E71's user manual provides instructions with diagrams that show how the SIM card is to be installed. If you have lost the manual or no longer have access to it, a Google search can lead you to messages from other users that have the same problem or to a copy of the manual.
Carriers
T-Mobile and AT&T are the only national wireless service providers to operate GSM networks. The Nokia E71, released in June 2008, was designed for use on AT&T's network, but can also operate on T-Mobile's. Purchasing an unlock code from AT&T enables you to unlock the device and use it on T-Mobile's network. If you have switched from AT&T to T-Mobile, you must contact T-Mobile to provide the company with the SIM card number. Neglecting to do this will result in the phone failing to connect to the carrier's network, which is easily assumed to be the result of a failed connection between the phone and its SIM card.
Network Issues
Sometimes, what appears to be an inability for the Nokia E71 to access its SIM card is actually a problem with the wireless provider's network. For example, a carrier's network can become inoperable under extreme conditions, such as excessively high network traffic or stormy conditions. These conditions can cause excessive delays in data transmissions or SIM card problems. In these situations, your only option is to wait for the situation to resolve itself.
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