HoudahGeo offers several options for geocoding your photos: automatic using GPS track logs, using GPS waypoints, using built-in maps, using Google Earth, etc.
One of the lesser known options is geocoding from reference photos (aka. gap fill geocoding). The basic idea behind this technique is pretty simple. Your iPhone creates geocoded photos. You may however find the camera lacking when compared to your regular digital camera. Your preferred camera on the other hand lacks a GPS chip. HoudahGeo can match up geocoded photos from your iPhone with photos taken around the same time using your regular camera. It can thus assume both were taken at the same location.