Like they have said, no alt key is needed. When you are in "phone mode" (using the phone) there isn't a need to hit the alt key when you are using the standard phone keys 0-9 * & #).
Also...
When you need to dial a name, such as 800Blackberry (example) you hold down the alt key for the letters. so you would dial 800 then press and hold the alt key and type BLACKBERRY and then hit send.