Nextel's Wi-Fi plans aren't about hot spots, but about better in-building coverage: Nextel has partnered with RadioFrame Networks to allow its iDEN network standard to have better coverage inside buildings, while also providing 802.11b service for wireless LANs. The two are basically unrelated, but RadioFrame can add iDEN cards to Nextel corporate customers alongside their Wi-Fi cards. GSM, 802.11a, and 802.11g will follow, according to this story.
This isn't so much about Nextel branching into Wi-Fi. Rather, it's about extending their voice service by reselling a product that provides better voice performance while answering the wireless LAN need.