Add Mobile Input to register.phtml

                <!-- Mobile Custom Customer Attribute -->
                <li>
                    <label for="mobile" class="required"><em>*</em><?php echo $this->__('Mobile Number') ?></label>
                    <div class="input-box">
                        <input type="tel" autocapitalize="off" autocorrect="off" spellcheck="false" name="mobile" id="mobile" value="<?php echo $this->escapeHtml($this->getFormData()->getMobile()) ?>" title="<?php echo $this->__('Mobile Number') ?>" class="input-text required-entry" />
                    </div>

                </li>