Can I use my regular 3.5 mm earphones with an iPhone?
Yes, you can use any earphones with a 3.5mm audio jack. I'm surprised you did not just try it out :)

I thought I'd add some additional background information I just read about in a report on yet another Apple-Samsung patent case, Apple holds a patent on an audio jack which has the circuitry to detect the type of headphones plugged in, and I can only assume this is what they actually use in their iPhones.