#1. "RE: WU-1A equivalent for D5100" In response to Reply # 0
San Diego, US
I'm fairly certain the Eye-Fi SD cards will work with the D5100. I have not used them personally, but I have read of people on the internet using them successfully. If you look up "Eye-Fi" you will find more information on it. They don't sound like great SD cards, and they're expensive. But it's a possibility.
However, I don't know of anyone using them for the purpose of putting photos on their smartphone. I don't know if my Android shows up on my wireless network, or if I can make it show up. I tried this morning and couldn't get my smartphone to show up on the network despite using the WiFi on it.