Wi-fi, smartphone, iPhone questions?

Wi-fi isn't only for phones. It was made for laptop use orignally, not phones. And few people have wireless data plans for laptops, so Wi-fi is still in high demand. Also, Wi-fi speeds are generally faster than those of a network's wireless data plan, which is better if you need to download larger files or such. Smartphones access the internet through both, satellite and cell towers. It all depends on who your wireless provider is. GSM networks(AT&T/T-Mobile) use towers, while Verizon and Sprint stick to satellites. The message you received was probably just telling you that the Wi-fi would be dominant over the networks data plan.