Apple Has Already Approved The Official Google Voice App For iPhone
techcrunch.com
techcrunch.com
Even if Google decides to implement a VOIP service as part of GV, users will still need to have a carrier data plan to make use of it, and if a lot of people switch to data-only plans to use GV, carriers will simply respond by further increasing the cost of "unlimited" data plans...
IIRC, on Verizon my parents paid $30/month extra -- above and beyond the data plan -- for unlimited texting, because some of their business contacts are inveterate texters who won't or can't currently switch to email on their phones.
They are already paying Verizon's top tier prices, including for unlimited data, and then get walloped an extra $360 a year for the privilege of cramming brief messages into the spare room of the network's status/heartbeat messaging.
I mentioned a Voice account (or two), but that was a bit too far afield for them, at the time (and imagine their contacts' confusion over a second number). Nonetheless, saving $30/month seems like a bit of motivation, in general.
"Pizza."