What is the ruling on honoring one's parents by phone and being content with calling every month or two, given the cost of calls, and does the obligation of calling differ between males and females, or in the frequency of calls?

The true Sharia has given great importance to maintaining kinship ties, and has made custom the reference for determining the extent, type, and manner of maintaining these ties. Therefore, your phone calls to your parents are considered a form of maintaining kinship. However, you should not limit yourself to phone calls, but rather connect with them through visits and financial assistance as much as you can, unless phone communication is the only possible means. The evidences obligating the maintenance of kinship ties include both males and females, and there is no text that differentiates between them in the extent of these ties. It is required from everyone, children and parents alike.