How to construct a telephone number link on Android that includes an extension
Please take a look at this forum for several examples of people overcoming the problem you're describing.
Summary: It would appear that there are 2 general ways to do this.
- You can add a series of
,characters, which will create a brief pause, or - You can add a
wcharacter, which prompts the Android phone to wait for you to press a second button before it will dial the extension.