I had a defective Chinese old mobile and due to its sound quality,light effect i tried to use it as a simple music player.
it was not of any use because the sim slot is defective & some number keys/ buttons are not working.so i decided to convert it as a music player.
We Observed

Step 1: Make Settings and Preparation:-

1.Copy Songs and videos to the mmc and insert it in the phone.
2.Charge the battery to 100%.
3. Set a Shortcut key to open Music Player Directly.
4. Adjust "Backlight".
5. Switch on "Bluetooth"(For file Transfer)
6. Set a beautiful picture as a wallpaper.
7.Set mmc as Defult storage in Bluetooth and music player if required.

Step 2: Requirements:-

1.Old mobile(with mmc,working important buttons and all basic things like battery,charger,Bluetooth enabled,)
2.Push button switches(i used 11)
3.wires
4.soldering iron.
5.soldering skill
6.Some Small Chinese phone speakers.
7.Amplifier Circuit from old laptop speakers.
8.Power supply for amplifier Circuit.

Step 3:

#Open screw and dissemble front and back cover/ Panels carefully.

#If speaker of Your mobile is not good, then replace it with A better small speaker(Of any Chinese Mobile).
"Take wires of speaker longer then before because we will attach it in the front panel,And attach a 3.5mm female jack as picture above"

Step 4: Modify the Keyboard:-

luckily important keys like volume,option/menu,back,select, Arrow and some number key are working fine.
and thats why i decided to convert it as a music player.
The keyboard of the cellphone was a bit damaged.So I decided to build a new keyboard with the Push Button Switches.I already had enough switches because i purchased more then required for this awesome instructable.

I removed the whole keyboard from the front of the cell phone.and polished the small contacts there are located under the keyboard and soldered two wires on each pair of contacts as shown in above picture 2.
The soldering part is very difficult.I used total of 11 switches/buttons.
1.up
2.down
3.left
4.Right
5.Enter
6.Option
7.Option 2
8.Back
9.Power on/off
10.volume +
11.volume -
Now attach Push button switches carefully.and check all key and its function.

Small but useful tip:- In the soldering process if you want to reduce difficulty and soldering mistakes,switch on your cell phone,and then solder the wires.And after completing the soldering process Check everything and fix the wires with the help of hot glu.

Step 5: You Can Add More Speakers With Amplifier Circuit:-

Now If you want to add more speakers as i did at both side then use a amplifier circuit (I used circuit from an old laptop speaker with external power supply)
For input you can use 3.5mm jack which is attached with the back speaker's wire(in step 2).
and for power supply add a charger of 5v with the amplifier.

i attached total of 3 Chinese speaker (as shown above).And Computer speaker Through defult Audio jack(As shown in below images).

Step 6: Result of Hardwork:-

Now Everything is ready.Make outer body and Fix every thing at their place (Everything explained in the first picture Above).
Note:-
(1)Every phone is different then other so i am not giving the size info and details.
(2)I don't have 3d printer so i used Thick Card bord to make the outer body.You can use Wood and make the body of the required dimension & size.