You may need to configure the APN to use Zello. In the app, open Connection > Connection APN and choose Detect APN settings.
If this doesn't work, you may need to contact your mobile operator to get the correct settings.
We collect working apn settings here.
You can also generally find the correct APN by doing an online search for "APN blackberry 'your wireless provider'".
Note that CDMA networks (like Sprint or Verizon) don't require APN settings.