Different companies define different dial rules on the PBX in their VOIP system, for example, company A defines that all the dial sequences should begin with 9, then the call will be sent out. User can choose to dial 9 before dial the phone number every time they make calls, or user can make the phone precede 9 before every sequences they dialed. Here introduces two methods to precede a number before the dial sequence.

1 Use Dial Plan

All the Flyingvoice IP phones support Dial Plan, user can use subsequence substitution way to precede 9 before each  dial sequence.
A subsequence of keys (possibly empty) can be automatically replaced with a different subsequence using 
an angle bracket notation: ‘<’ dialed-subsequence ‘:’ transmitted-subsequence ‘>’.
So, for example, “<:1650>xxxxxxx” would match “5551212” and transmit “16505551212”.
If user wants to preced a number before the dial sequence, just make the dial rule to be <:9>xxxxxx.

Notice: only when the dial sequence matches the corresponding dial rule, can the dial rule take effect, and 9 willl be added before the dial sequence.
For example, in the upon picture, any dial sequence with 6 characters will begin with 9 when user make calls.
If the length of the dial sequence is longer or shorter than 6, phone won't add 9 before the sequence.

Use Dial Prefix Option

In SIP Account-->Line x(1/2/3/4/5) page, Advanced column, enter the number in Dial Prefix option. For example, if you would like to precede 9 before the dial sequences, enter 9 in the option. User can precede any number they need before the dial sequence.