I haven't experienced any ads, but I notice that on AT&T-based TracFones, I'm routed to a different generic 411. I just called it now and it sounded like an Indian gal, someone I'd talk to if I were calling TracFone. That's fine for me, I hardly ever call 411, but I think the ads are a bit much if that's what they're switching to. We're paying for our service with TracFone, so that should exclude ads.
As a side note, on Verizon-based TracFones, 411 gets the same generic 411. However, dialing 1411 gets you Verizon Wireless directory assistance. That's a nice perk because I get to talk to someone at least in the US, sometimes even local.
Castrol EDGE 5W-30 is my drug of choice.
Primary: iPhone 6 64GB, Galaxy Note 3, Galaxy Avant: 5 lines, 3x $5 Android web, 1x $2.99 T-Zones
Secondary: iPhone 5 & Motorola E LTE: TracFone (Verizon)
Mobile Broadband: ZTE Z915 LTE hotspot (5GB for $10) + iPad Mini Retina w/ T-Mobile LTE