When i try to Activate The Call Forwarding by changing the Voice Calls number i get the message Request Not Successful. Due to this when a second person calls my cell when i use it, it goes straight into voicemail.

you have to call your service provider to resolve this problem

Hi Shailesh,
I have steps below on how to turn it on and since your concern is to turn it off please do the vice versa. Hope it helps.
Forward calls to your voicemail or another phone number Your phone is ringing, but you can't answer? Let the call go to your
voicemail, or forward it to another number. Call forwarding is a
network service.
1. Select settings > calls > call forwarding.
2. Select when to forward the incoming voice calls:
all voice calls - Forward all calls.
if busy - Forward when busy.
if not answered - Forward when not answered.
if out of reach - Forward when the phone is switched off or out of
network coverage for a certain length of time.
if not available - Forward when busy, when not answered, when the
phone is switched off, or when out of network coverage.
3. Select activate > to voice mailbox or to other number.
4. If if not answered or if not available is selected, set the length of
time after which a call is forwarded
Nokia 311 User Manual Page 30 Forward Calls To Your Voicemail Or...

go to the call settings then click on the call divert option then click divert all voice calls then on that select the option as divert to another number then feed the number inside the tab now click ok check the status now if it says activate then its ok. If not activated then contact your service provider to activate the call divert for your number . because they may block divert optoin for your number

As your using samsung sch u350 you can forward your call by following simple step.Go to main menu select settings after that select call settings after that select call divert after that select divert all voice calls then activate you can give your another number there you can recive calls.Other wise you can forward it to voice mailbox.Your old number will recive only message .

Cordless phones can not 'forward' a call to an outside line.
Forwarding must be controlled by the ATT, Verizon, or landline provider.
Please contact your provider to determine if you have call forwarding feature built into your service package.

Then, follow the instructions of your landline phone provider.
Here is the instructions for Verizon:


Activating Call Forwarding
You can activate Call Forwarding whenever you want your calls to be sent to another phone, including a mobile phone. Once activated, all your calls will be sent to the forwarding number you request. Each time a call is forwarded, you will hear one short reminder tone on your home phone, but you will not be able to answer the call from your home number.

1. Lift your telephone's receiver and listen for a dial tone.
   
   
2. Press .
   In some areas you must use
   Dial 1172 on rotary or pulse-dialing phones.
   
   
3. When you hear the tone, set or change the Call Forwarding number by dialing the telephone number where you want your calls transferred.
   You will hear the number you entered ring. When the number is answered, Call Forwarding is activated.
   
   
4. If the call is not answered or the line is busy, hang up and call the number again within two minutes.
   You will hear two short tones telling you that Call Forwarding is activated.
   
   
5. Hang up the receiver.

Go to settings, phone, voice calls, forwarding, unavalible or no answer. In there you can select the number of seconds. Each ring is equal to 5 seconds.

Open BlackBerry Call Forwarding Options
To access your BlackBerry call forwarding options screen, click the green Send key and then open the menu options by clicking the BlackBerry Menu key. Scroll down and select Options.
You'll then be presented with a list of your BlackBerry's Phone Options, which include Call Forwarding. Click on this option and wait a few seconds for the call forwarding screen to populate.
Enter a New BlackBerry Call Forwarding Phone Number
Before you can forward incoming calls via BlackBerry, you first need to enter the number you want calls to be forwarded to.
On the main Call Forwarding options screen, click your BlackBerry Menu key and choose New Number. A dialogue box will then appear asking for the number to which your calls will be forwarded. Type in the 10 digits and click the trackball to save the number.
If you mistyped the new call forwarding number and you need to correct it you can click the BlackBerry Menu key on the main call forwarding screen, choose Edit Number, scroll to the number you wish to modify, click the trackball again and choose Edit from the available options. From there, you can make your desired corrections. To save the changes, simply click the trackball one more time. You'll then be returned to the Edit Forwarding Numbers screen. You can reach the main Call Forwarding option screen by clicking the BlackBerry Escape key once.
Enable BlackBerry Call Forwarding, Tweak Settings
On the main BlackBerry Call Forwarding screen, you have two options for call forwarding: 1) Forward All CallsForward Unanswered Calls. Below the latter option, you have three more choices: A) If Busy; B) If No Reply; and C) If Not Reachable.
By default, your device is set to Forward Unanswered Calls to your carrier's voice mail box in all instances.
BlackBerry Forward Unanswered Call Options
Forwarding every call that comes in to your device is simple; you just fill in the circle next to Forward All Calls and then specify the number to which you wish to direct calls from the corresponding drop-down menu. To save any changes you make, click the BlackBerry Escape key and confirm the changes when prompted.
Forwarding calls in specific situations is a bit different, but it's no more difficult. The first thing you want to do is ensure that the circle next to Forward Unanswered Calls is filled in. (Again, this circle will be filled by default unless you modified your settings.)
To forward only the calls that come in while you're already on the line, click on the If Busy option to open the drop-down menu and then choose the number to which you want to forward your BlackBerry calls. If that's the only call forwarding option you wish to modify, click the BlackBerry Escape key and confirm the change when prompted.
If you want to forward calls that come in while you're, say, in another room and away from the phone, change the number associated with the If No Reply option and save your changes.
If you want to receive calls when your BlackBerry is turned off or you're otherwise unreachable, modify the number settings next to the If Not Reachable option and again save your changes.
When BlackBerry call forwarding is enabled, you'll see a small icon, which looks very much like the missed call icon, appear on your BlackBerry home screen.
Finally, if you wish to return to your device's default settings, simply fill in the circle next to the Forward Unanswered Calls option and set the number for all three options (If Busy, If No Reply and If Not Reachable) to your wireless carrier's voice mail digits.

Activating Call Forwarding

You can activate Call Forwarding whenever you want your calls to be sent to another phone, including a mobile phone. Once activated, all your calls will be sent to the forwarding number you request. Each time a call is forwarded, you will hear one short reminder tone on your home phone, but you will not be able to answer the call from your home number.

1. Lift your telephone's receiver and listen for a dial tone.


2. Press *7 2.
In some areas you must use 72#
Dial 1172 on rotary or pulse-dialing phones.


3. At the tone, dial the telephone number where you want your calls transferred.
You will hear the number you entered ring. When the number is answered, Call Forwarding is activated.


4. If the call is not answered or the line is busy, hang up and call the number again within two minutes.
You will hear two short tones telling you that Call Forwarding is activated.


5. Hang up the receiver.

Deactivating Call Forwarding

Turn Call Forwarding off when you want to receive calls on your home phone.

1. Lift your telephone's receiver and listen for a dial tone.


2. Press * 73.
In some areas you must use 73#
Dial 1173 on rotary or pulse-dialing phones.


3. Listen for two short tones.
Call Forwarding is now off and you will receive your calls at your home number.

It is usually under message menu. try under setting of this menu. Alternatively you can use one more method that will sound funny but works. Press and hold the No. 1 key and see which number it is dialing. If the voicemail is already set it will be shown to you, edit this from the phonebook to your desired number. If the Voicemail has not already been set you will be prompted to enter you the voicemail number. Fill in the desired number there.

only calls can be forwarded but you can try your area code + number