I always forget the soy milk.

How nice would it be if, whenever I walked into the grocery store, a text message popped into my iPhone reminding me: “Dude, do yourself a favor and remember to get the soy milk.”

Michael Massie, a Milwaukee software developer and designer, and Bob Ralian, a local engineer and entrepreneur, are building a solution that delivers gentle reminders to your smartphone.

Airrand.com, which launched its beta late last month, is a smart to-do list that sends text message reminders when you visit specific locations. The Web service does this by linking into Foursquare, a location-based mobile app that people use to share where they are with friends.

By visiting Airrand.com, setting up an account and tying it to foursquare, users can build lists of things they need to do based on categories like “grocery store,” “school” or the “gym.”

Then when they use the Foursquare app to electronically check into these kinds of locations, Airrand.com sends an e-mail, text message or both with the reminders programmed ahead of time. So now, when I check into the grocery store, Airrand.com texts me with a link leading to the to-do list.

Massie said the inspiration for Airrand.com emerged during conversations with Foursquare executives while discussing ways to enhance the app. Currently, the Foursquare smartphone software lets its users leave tips for friends, and Massie wanted to expand on that functionality.

“What we were looking for was a very disposable to-do list,” Massie said.

Airrand.com also has a “couples” feature that lets two people link their to-do lists. Now, whoever makes it to the store first is reminded to pick up the soy milk.

“It’s a great way to double-team a to-do list,” Massie said.

The service works with any Web browser and Foursquare-friendly smartphone, which includes Android mobiles and Apple iPhones. Massie noted that he wanted Airrand.com to start its life with Foursquare because it’s a popular social mobile app, and “they have the most active user base.”

The technology behind Air rand.com could support smart coupons someday so, eventually, when I check in and the soy milk reminder kicks in, I could get a discount off the weekly purchase of Silk.

But for now, the online mobile service will remain a side project that Massie and Ralian grow while balancing family and full-time jobs.

“We’re going to keep it free and may periodically make feature updates, but for now it will be an as-is product that we’d love for others to enjoy with us,” Massie says.