Os oes angen rhagddodiad deialu arbennig (e. e. os ydych yn defnyddio switsfwrdd ffonau) cewch benodi hynny yma. Deialir y rhagddodiad union cyn y rhif ffôn. Os oes gennych switsfwrdd ffonau, tebyg bydd angen ysgrifennu "0" neu "0," yma.
If you need a special dial prefix (e. g. if you are using a telephone switch) you can specify it here. This prefix is dialed just before the phone number. If you have a telephone switch, you probably need to write "0" or "0," here.