I don't believe I was able to get service when I was there (I have Verizon). If you need GPS and want to use your phone, I would recommend downloading an offline map app such as this (Android-not sure if there's an iPhone equivalent).
https://play.google.com/store/apps/d...smand&hl=en_GB

And then downloading the Barbados maps and using your GPS like that.

For phone, if your hotel has wifi, you can use Google voice
http://google.com/voice

and an app such as this
https://play.google.com/store/apps/d...oveip&hl=en_GB

Which will allow you to call the US/Canada for free (provided the internet connection is decent enough).