Andre -
Most likely, you're not going to find what you're looking for in the RR database. Since the services you mention are not as interesting to most hobbyists, these channels and frequencies are not well documented in the database. This means that you'll have to do some research and trial-and-error on your own. Once you figure out the channels you're interested in, you can submit the data and I'll add it to the database for you and others to share.
In the case of the business systems referenced below, you'll have to create favorites lists for the HP-1 manually to even begin to monitor them. I'll tell you that the HP-1 is not the best scanner to do this sort of sleuthing, but it can be done. Consider investing in a RTL SDR dongle instead. This is a small, inexpensive device that connects to a USB port on your computer and uses free software (downloaded separately) to tune specific bands and frequencies. It makes identifying these types of systems much much easier. But I'll warn you that it takes some pretty serious computer skills to get it to work. There is software available to decode these DMR systems to so you can hear what they're saying.
Here are some specific comments about the services you mention:
Electric Utility - which utility provides service in the area you're interested in? Is it SCE&G, or Berkeley Electric, or some other utility? SCE&G crews use talkgroups on the Palmetto 800 trunked system and some may even be identified as being in use in your area. Take those identifications with a heavy dose of salt because I'm not confident they are 100% accurate. But in general, the SCE&G talkgroups are in the range of 1000-6000. Berkeley Electric most likely operates on the SC PSA trunked system (link below), as do most electric co-ops in the state. Enable the sites closest to you and see what you hear. You'll have to figure out how to enable your HP-1 to receive all active talkgroups on these systems (called a wildcard on most current GRE/Whistler scanners) so that you can hear talkgroups that are not currently listed in the database.
South Carolina Public Service Authority Trunking System, Various, South Carolina - Scanner Frequencies
Taxis - most taxi services have traditionally operated on a conventional VHF radio system. Sometimes it's a typical repeater, other times it's a more confusing duplex system that prevents drivers from talking directly to each other, only the dispatcher. Check the FCC licenses for your area, and enable only the Business Conventional licenses to be shown. Look through them and you might find a license for the company you're interested in. Some cab companies use different types of "encryption" to prevent other cab companies from stealing fares. Some might be using a digital technology like DMR, or mobile telephones (most likely). Some might also use local business trunked systems. Look for antennas on the cab vehicles to get a clue as to whether a radio is in use and if so, what band it might be.
Towing companies are similar to cab companies in how they communicate. Most probably use mobile phones these days. Those that don't probably use a local business trunked system, so you won't find a specific FCC license for them. Charleston Wireless, Radio Communications of Charleston, Mount Pleasant Radio Co and Mobile Communications of Charleston all appear to have business trunked systems licensed in Berkeley Co. Most are UHF. Search between 451-455 and 461-465 and see what you hear. You'll probably hear a lot of buzzing noises and those are most likely DMR or NXDN digital radio systems. There are probably some analog LTR systems out there too. Part of the fun of scanning is discovering and mapping these systems.
Berkeley Co School District appears to operate a trunked radio system in the UHF band too. FCC licenses WPTA426 and WQOD435. Again, this might be some flavor of analog LTR or a digital system. I would guess this is the system that the school buses use.
Feel free to PM me for more details on your question.
Brian
