Add function in a custom attribute on save - Magento 1.9

I want to do some function in my custom attribute on saving in customer/account/edit,my idea is 1-rewrite the editPostAction() or 2- create an observer on this saving event.

So i rewritted the editPostAction() then i get the param but i dont know how to implemente my function on saving.

My function :

Mage::getModel('custom_telephone/telephone')->validatePhoneNumber()

customer/account/edit:

<li>
   <label for="custom_telephone" class="required"><em>*</em><?php echo $this->__('Phone number') ?></label>
   <div class="input-box">
       <input type="text" name="custom_telephone" id="custom_telephone" value="<?php echo Mage::getModel('custom_telephone/telephone')->removePrefixePhoneNumber($this->escapeHtml($this->getCustomer()->getCustomTelephone())) ?>" title="<?php echo Mage::helper('core')->quoteEscape($this->__('Phone number')) ?>" class="input-text validate-number validate-length maximum-length-10 minimum-length-10 required-entry" />
   </div>
</li>

editPostAction() :

public function editPostAction()
    {
        if (!$this->_validateFormKey()) {
            return $this->_redirect('*/*/edit');
        }

        if ($this->getRequest()->isPost()) {
            Mage::log('Start postAction');
            /** @var $customer Mage_Customer_Model_Customer */
            $customer = $this->_getSession()->getCustomer();

            /** @var $customerForm Mage_Customer_Model_Form */
            $customerForm = $this->_getModel('customer/form');
            $customerForm->setFormCode('customer_account_edit')
                ->setEntity($customer);

            $customerData = $customerForm->extractData($this->getRequest());

            $errors = array();
            $customerErrors = $customerForm->validateData($customerData);
            if ($customerErrors !== true) {
                $errors = array_merge($customerErrors, $errors);
            } else {
                $customerForm->compactData($customerData);
                $errors = array();

                // If password change was requested then add it to common validation scheme
                if ($this->getRequest()->getParam('change_password')) {
                    $currPass   = $this->getRequest()->getPost('current_password');
                    $newPass    = $this->getRequest()->getPost('password');
                    $confPass   = $this->getRequest()->getPost('confirmation');

                    $oldPass = $this->_getSession()->getCustomer()->getPasswordHash();
                    if ( $this->_getHelper('core/string')->strpos($oldPass, ':')) {
                        list($_salt, $salt) = explode(':', $oldPass);
                    } else {
                        $salt = false;
                    }
                    if ($customer->hashPassword($currPass, $salt) == $oldPass) {
                        if (strlen($newPass)) {
                            /**
                             * Set entered password and its confirmation - they
                             * will be validated later to match each other and be of right length
                             */
                            $customer->setPassword($newPass);
                            $customer->setPasswordConfirmation($confPass);
                        } else {
                            $errors[] = $this->__('New password field cannot be empty.');
                        }
                    } else {
                        $errors[] = $this->__('Invalid current password');
                    }
                }
                //************ my add *************
                $tel = $this->getRequest()->getPost('custom_telephone');
                $telTransformed = Mage::getModel('custom_telephone/telephone')->validatePhoneNumber($this->getRequest()->getPost('custom_telephone'));
                if($this->getRequest()->getPost('custom_telephone')) {
                    $tel = $telTransformed;
                    Mage::log($tel);
                }
                //*********** End my add ***********                    

                // Validate account and compose list of errors if any
                $customerErrors = $customer->validate();
                if (is_array($customerErrors)) {
                    $errors = array_merge($errors, $customerErrors);
                }
            }

            if (!empty($errors)) {
                $this->_getSession()->setCustomerFormData($this->getRequest()->getPost());
                foreach ($errors as $message) {
                    $this->_getSession()->addError($message);
                }
                $this->_redirect('*/*/edit');
                return $this;
            }

            try {
                $customer->cleanPasswordsValidationData();
                $customer->save();
                $this->_getSession()->setCustomer($customer)
                    ->addSuccess($this->__('The account information has been saved.'));

                $this->_redirect('customer/account');
                return;
            } catch (Mage_Core_Exception $e) {
                $this->_getSession()->setCustomerFormData($this->getRequest()->getPost())
                    ->addError($e->getMessage());
            } catch (Exception $e) {
                $this->_getSession()->setCustomerFormData($this->getRequest()->getPost())
                    ->addException($e, $this->__('Cannot save the customer.'));
            }
        }

        $this->_redirect('*/*/edit');
    }