You may not be able to receive a text message for your initial log on. You will need to activate text messages once you have logged on successfully by going into the My Settings and within the Login & Security section, you will need to click on the Enable for text link.
If you still do not receive the One-Time Passcode after you have activated your mobile device, you will need to call your mobile carrier and make sure that you do not have short codes blocked. If you do have short codes blocked, you will need to request that your mobile carrier unblock short code access, or add the short code 44833 to the allowed short code list for your mobile device.