Will iPhone SE connect to a 802.11b/g router? I plan to purchase iPhone SE. The spec says the Wi-Fi module is 802.11ac (5 GHz band). However, my router is rather old - it supports 802.11b and 802.11g only (2.4 GHz band).

I cannot find information on whether a 802.11ac device can work in a backward compatible mode (i.e., on a lower frequency) with a 802.11b/g router or not.

So, will I be able to connect iPhone SE to a 802.11b/g router?
Absolutely.

Almost all wifi products are backwards compatible (I can't think of any that aren't). Specifically regarding the iPhone SE, the site GSM Arena lists the full specs for the iPhone SE's wifi modem: Wi-Fi 802.11 a/b/g/n/ac, hotspot.