I can see a tower, yet I still have no signal...

Have you ever been out somewhere and could not get strong enough signal to make a call, only being more frustrated that you can see a tower directly in front of you? There is an easy explanation. As you may recall, I have stated before how not all service providers use the same signal, and not all towers broad cast all signals. Let us take this a step further. We have also discussed in previous posts that there are carriers that operate on the same frequency. So, just for an example, let's say that you are traveling with a friend in a rural area and you are running late and are trying to contact someone at your destination to let them know. You redial several times only to realize that you do not have coverage in that area. Already frustrated that you are late and can not let anyone know, your frustration grows when your passengers phone rings and they take the call with no problems. You now know what carriers operate on what signals, and with this knowledge you realize that you are both using the same signal type. Why does only one phone work? This can also be easily explained. Cellular towers are quite costly to build and operate. Cellular companies often lease their tower usage to other carriers, and these leases are on a tower by tower basis not all inclusive. So, lets say for example that you have Sprint and your friend has Verizon. The reason they have service and you do not, is simply that the nearest tower is owned/operated, or leased for use for Verizon, and Sprint does not have a deal established to use that particular tower. I would like to say that this is just an example. I am not saying that Verizon has any more or less towers than Sprint, this could easily work the other way with Verizon not in a leasing arrangement with Sprint, or US Cellular, or any other CDMA service. There is a way to still be able to place this call. Most(not all) phones have an ability to switch on and off roaming capabilities. (Roaming simply means using another compatible signal other than your carriers, despite the common misconception that it is based on location.)If your phone has this capability you can choose to enable roaming, and make your call. Please be warned, depending on your chosen calling plan there is a good chance that you will be paying additional charges for using a competitors signal as your carrier will be charged more for the use of the tower that they are not in a lease with. No one wants additional charges, but in an emergency situation it is nice to know you have a back up plan. Most carriers have their handsets pre-programed not to roam unless the setting is changed by the end user. -but roaming is a topic for another posting.

What carriers are using what signals?

With so many carriers out there and many different signals, who is using what? I will tell you, grouping them by signal type. CDMA is what the US started with as the first cell phone signal, and therefore has the most coverage area, simply because we have been building the towers for that type of signal the longest. The more major carriers on this signal are: Verizon, Sprint, AllTel, and US Cellular. The next largest in coverage area(in the US) is GSM. These carriers include: Cingular (now AT&T) and Tmobil. The third major signal is IDEN and is primarily used by Nextel (now merged with Sprint). Please keep in mind there are exceptions to every rule, such as some companies have "world phones" meaning they can be swapped to and from CDMA and GSM. With this type of phone you can easily use the signal here or overseas, by just setting the device accordingly.

How do they make calls while I have no signal?

Have you ever been out some where and wondered how can this be? People beside you are talking away on their cell phones, and yet you have no service at all? There is a very easy explanation for this. Different carriers broadcast on different frequencies, such as radios operate on AM or FM signals, and unlike your radio where you can change what signal you wish to receive, your phone is designed to work with a specific signal to communicate with a specific carrier.
Why are there different signals when we all simply want to have a phone work anywhere possible? This again is easily explained. Competition is the main reason, every company want to be the best. The three biggest broadcasts used in the US are: CDMA, GSM, and IDEN. Each one has its strong and weak points just as anything else. CDMA is what the US had started with in the preliminary days of cellular. GSM is the signal most commonly used in Europe and Asia. IDEN is a slightly newer (in comparison) signal that has been made popular with a particular company boasting there 2-way walkie talkie service.
I would like to say right away that I am not affiliated with ANY cellular companies, however I have worked with most of them in the past, and that is where my information has come from. This blog is not to sell or sway your opinions in any way, shape, or form. I am making these postings simply so that you can make a more informed decision before you lock into that 2 year contract. I will NOT discuss rate plans or customer service, I will simply tell you how they work, and the advantages and disadvantages of the given carriers in different areas, and for specific needs. I do not believe that there is any one great carrier out there, as I have before stated each have there strong and weak points.