How would I plan an efficient route for several service calls within the city?

There is a few ways of doing it. The easy way is the old fashioned way. Get a map book. Write out your stops, and plot them. If you have like a ticket or something then you can place them in order. Another way is a get a large city map, and plot that way. Or a Zip code map would help. There is no free software that I know of. Some paid maybe. But who wants to sit and type each address.

I would make a customer list, and assign a map number to them. If they are B7 on the map then you can code it. Maybe put them on index cards, and pull them up when needed. Learning phone prefixes can also help sometimes. Some phone books have zip code, and or phone prefix locations in them. Some even have maps. Put something motivational, or inspirational on the radio. It used to help me get thru the day!