Dear fmshall: The reason to have someone come back in 6 months is because there is something on the mammogram that doesn't look particularly suspicious but the doctors want to be sure it does not change or take on more suspicious characteristics. You should discuss with your doctor about taking estrogen replacement. This is a controversial topic and you need to be certain that the benefits outweigh the risks as they pertain to you and your personal risk.
calcifications are very common in the breast, and can be due to many different things. Cancer is on the list. Certain patterns of calcifications are associated with certain conditions; so it's not unusual for the radiologist to want additional views, often with magnification. If those views show certain patterns that are considered innocent, and combined with the info that they haven't changed, it's generally considered ok, and perfectly safe just to keep an eye on them. Why they weren't pointed out to you before could mean that the previous radiologist was certain enough that they were ok that they weren't mentioned, or were mentioned in such a way that your doctor was comfortable that they were of no significance. Sometimes another radiologist just has a habit of being extra cautious.