If you have an Android phone and are having trouble with your voicemail PIN after changing carriers, you might need to change your Dual Tone Multi-Frequency (DTMF) tones. DTMF tones are the sounds used by your phone's keypad to dial numbers.

Here's how you can do it on most Android devices:

1. Tap the phone icon.
2. To open the menu, tap the three dots (or the More button) in the upper right of the screen.
3. Tap Settings.
4. Tap Call.
5. Tap DTMF tones.
6. Select the option for Long.

If the directions above don’t work, try these steps as they apply to some versions of Android:

1. Tap the phone icon.
2. Tap the Menu button (located in the upper right corner)
3. Tap Settings.
4. Tap Calls.
5. Tap Sounds and vibration.
6. Tap Dialpad Tones to enable.
7. Tap Dialpad tone length, and select the option for Long.