Why can't I set up BlackBerry messenger?

why my blackberry cannot set up blackberry messenger ?

If your BlackBerry is a legacy device, a non-BlackBerry 10 device, then it requires an active BES or BIS data service to use BBM. If you have such a data service, then check to see if the BlackBerry icon, the four "D"'s, are present near the signal strength bars. Try a WiFi connection if the BB icon is not present or the cell signal is lower than 2g.

If it is a BB10 device, then check to see if you have a good 3g or 4g signal or WiFi. It will work with 2g and somewhat under, but the connection may be unstable enough to make it too difficult to complete the BBM/BBID setup. Check to see if your data service provider is set up correctly for your device. Also check to see if your country or region isn't blocking access to BlackBerry's BBM service.

Maybe no internet connection available?

Typing with excellent touch board z10