Voicemail

Voicemail is a carrier feature. If your carrier supports Visual Voice Mail, you can set it up, and not have to call in to get it. If your carrier does not support Visual Voice mail, then the only option is to call in for it.

See here: link-> Check your voicemail on iPhone - Apple Support

Pure Talk does appear to support Visual Voice Mail. So I would contact them and ask why its not available on your device.

Link-> Wireless carrier support and features for iPhone in the United States and Canada - Apple Support

Voicemail, including visual voicemail, is a carrier feature.

Contact your cellular carrier.