Physically, memory cards are quite fragile pieces of high technology, susceptible to damage from various silly things like excessive heat, condensation, strong magnetic fields, physical damage from rough handling and/or bending.

Given the natue of mobile memory card products, they are constantly being taken in and out of some form of interface with a mobile phone, a camera, a laptop, or desktop PC, or a separate memory card reader. The number of different devices they have to be able to interact with is in the thousands. It is not too surprisingly, then that sometimes the state of the file system on the memory card can get damaged.

This may happen for a number of different reasons, including:
- Removing the card from a device whilst an application is trying to read/write to it.
- Battery drain on a device whilst in use meaning an insufficent voltage failure whilst writing to the card.
- Poor implementation of the MMC standard on the device using the card.
- Poor connectivity software drivers on the device or the Windows PC/Mac.
- Physical damage like card or device being dropped, bent, getting wet etc.

As often as not, the problem is not terminal for your memory card, but just a software issue ( or in physical terms, it could be called "a temporary disalignment of the all the bits and bytes on the card"). The fix for this problem is the same as for any other file storage device (like a floppy or hard drive) with corrupt or invalid file system, namely; re-format the file system.

The following codes are the standard GSM codes for various network services. Most Nokia phones have easier ways to activate them through the menus. Check the guides for your model.

Call Diverting

All
To Activate: * * 21 * NUMBER # [SEND]
To Cancel: # # 21 # [SEND]
To Check: * # 21 # [SEND]
No Answer
To Activate: * * 61 * NUMBER # [SEND]
To Cancel: # # 61 # [SEND]
To Check: * # 61 # [SEND]
Unreachable
To Activate: * * 62 * NUMBER # [SEND]
To Cancel: # # 62 # [SEND]
To Check: * # 62 # [SEND]
Busy
To Activate: * * 67 * NUMBER # [SEND]
To Cancel: # # 67 # [SEND]
To Check: * # 67 # [SEND]
To Cancel All Call Forwarding # # 002 # [SEND]

Diverting Data Calls

All
To Activate: * * 21 * NUMBER * 25 # [SEND]
To Cancel: # # 21 # * 25 [SEND]
To Check Status: * # 21 # * 25 # [SEND]
No Answer
To Activate: * * 61 * NUMBER * 25 # [SEND]
To Cancel: # # 61 * 25 # [SEND]
To Check Status: * # 61 # * 25 # [SEND]
Unreachable
To Activate: * * 62 * NUMBER * 25 # [SEND]
To Cancel: # # 62 # * 25 # [SEND]
To Check Status: * # 62 # * 25 # [SEND]
Busy
To Activate: * * 67 * NUMBER * 25 # [SEND]
To Cancel: # # 67 # * 25 # [SEND]
To Check Status: * # 67 # * 24 # [SEND]

Diverting Fax Calls

All
To Activate: * * 21 * NUMBER * 13 #[SEND]
To Cancel: # # 21 # * 13 # [SEND]
To Check Status: * # 21 # * 13 # [SEND]
No Answer
To Activate: * * 61 * NUMBER * 13 # [SEND]
To Cancel: # # 61 * 13 # [SEND]
To Check Status: * # 61 # * 13 # [SEND]
Unreachable
To Activate: * * 62 * NUMBER * 13 # [SEND]
To Cancel: # # 62 # * 13 # [SEND]
To Check Status: * # 62 # * 13 # [SEND]
Busy
To Activate: * * 67 * NUMBER * 13 # [SEND]
To Cancel: # # 67 # * 13 # [SEND]
To Check Status: * # 67 # * 13 #[SEND]

Call Barring

Before you can activate these barring services you will need a barring code from your service provider. Call Barring can not be activated if Call Forwarding diverts are already in use.

All Calls
To Activate: * 330 * BARRING CODE # [SEND]
To Cancel: # 330 * BARRING CODE # [SEND]
To Check: * # 330 # [SEND]
All Outgoing Calls
To Activate: * 333 * BARRING CODE # [SEND]
To Cancel: # 333 * BARRING CODE # [SEND]
To Check: * # 333 # [SEND]
All Incoming Calls
To Activate: * 353 * BARRING CODE # [SEND]
To Cancel: # 353 * BARRING CODE # [SEND]
To Check: * # 353 # [SEND]
All Outgoing Calls
To Activate: * 33 * BARRING CODE# [SEND]
To Cancel: # 33 * BARRING CODE # [SEND]
To Check: * # 33 # [SEND]
All Outgoing International Calls
To Activate: * 331 * BARRING CODE# [SEND]
To Cancel: # 331 * BARRING CODE # [SEND]
To Check: * # 331 # [SEND]
All Outgoing International Calls Except To Home Country
To Activate: * 332 * BARRING CODE# [SEND]
To Cancel: # 332 * BARRING CODE # [SEND]
To Check: * # 332 # [SEND]
All Incoming Calls
To Activate: * 35 * BARRING CODE # [SEND]
To Cancel: # 35 * BARRING CODE # [SEND]
To Check: * # 35 # [SEND]
All Incoming Calls When Outside Home Country
To Activate: * 351 * BARRING CODE # [SEND]
To Cancel: # 351 * BARRING CODE # [SEND]
To Check: * # 351 # [SEND]
Canceling All Call Barring # 330 * BARRING CODE # [SEND]

Call Waiting

To Activate: * 43 # [SEND]
To Deactivate: # 43 # [SEND]
To Check: * # 43 # [SEND]

Calling Line Identity

Outgoing
To Activate: * 31 # [SEND]
To Deactivate: # 31 # [SEND]
To Check: * # 31 # [SEND]
Incoming
To Activate: * 30 # [SEND]
To Deactivate: # 30 # [SEND]

BY RAJAGANAPATHI.S

Alcatel

IMEI number: * # 0 6 #
Software version: * # 0 6 #
Net Monitor: 0 0 0 0 0 0 *

Bosch

IMEI number: * # 0 6 #
Default Language: * # 0 0 0 0 #
Net Monitor: * # 3 2 6 2 2 5 5 * 8 3 7 8 # #

Dancall

IMEI number: * # 0 6 #
Software version: * # 9 9 9 9 #
SIM card serial number: * # 9 9 9 4 #
Information about battery status: * # 9 9 9 0 #
Selftest (only Dancall HP2731): * # 9 9 9 7 #
Show version configuration: * # 9 9 9 8 #
Net Monitor: * # 9 9 9 3 #

Ericsson

IMEI number: * # 0 6 #
Software version: > * < < * < * Default Language: <>
Enter to phone menu without SimCard - after Wrong PIN: press NO: * * 0 4 * 0 0 0 0 * 0 0 0 0 * 0 0 0 0 #
Information about SIMLOCK: < * * <> * < < * < * Default Language: <>
Enter to phone menu without SimCard - after Wrong PIN: press NO: * * 0 4 * 0 0 0 0 * 0 0 0 0 * 0 0 0 0 #
Information about SIMLOCK: < * * < 

Here is a way to Unlock your phone which is Service Provider locked, without to know SP Lock code.

First of all, PIN CODE MUST BE ON, then press:

C

C and hold until it clears display
* and hold until start to blink
* and hold until start to blink
04*
*
*
#

Each time you turn your phone OFF it resets the lock, so this need to be done each time you'll turn your phone ON

The phone now says: PIN CODE CHANGED (or ACCEPTED) and the SIM card is accepted until you restart the phone again.

NOTE: On version 5.04 onwards Nokia has removed this option.