I don't think it's unreasonable to expect that a core feature (like voice mail) should work out of the box with no additional installations on my part.
no, he wanted voicemail. T-Mobile decided to require a different app.
That's all he says. Nowhere in the post he says voicemail didn't work - he implies he wanted an app to get his Voicemail like iOS. The regular voicemail stuff just works on any stock Android GSM phone - you get a notification for new ones and you can tap that or long press 1 to go to carrier voice mail box for your old VMEs.
Nitpicking much? iOS started the Visual Voice Mail thing. No GSM, non-iPhone user is used to using Visual Voice Mail App - they pretty much tap the VME notification or long dial 1 to get to voice mail - that still works on any unlocked Android with any GSM carrier.