I was with EE, when I received a voicemail, I would receive a text with the callers number. The text would show the name of the caller if they were in my contact list. Smarty just send a text with ...
Okay TomKNRead, just call the SMARTY voicemail service on 123 (from your SMARTY SIM), then listen to the voicemail assistant for options to enable SMS alerts, for new voicemail messages.
Updated:
Sorry TomKNRead, overlooked your idea about showing the caller's number in the voicemail SMS alert.
I'm sure this used to be included, before Three UK upgraded the voicemail service, which happened within last 12-months.