I am pretty confident that most of us have Skype on our computers. It is widely known as the 'communicator' for the world where one only need to pay a minimum to make a call to another in another country without a fuss. Personally I am a Skype user too. In fact, I often use it without even thinking much about the price until recently.
From my point of view, Skype charges a fraction of what I used to pay to make an overseas call. I used to pay a monthly line rental of around £30 for 600 minutes and I would have to buy a calling card in addition to that. Previously the purchase of a calling card was not necessary on O2 UK because you could call 0870, 0844 or even 0845 numbers to get accessed to an overseas number. Unfortunately O2 do away with that facility. Well, Skype has replaced calling cards to an extend.
If you have a data plan, you could download Skype and start making calls using VOIP service. The trouble is that you need to have good signals for data. Never think that GPRS connection will be sufficient. You would need a minimum of a 3G signal to have smooth conversation. If you are using Skype from 3UK, it is a different ball game all together. With 3UK, you are actually physically making a telephone call and not using data at all so you do not need good coverage for the service - Mere 2G connection will do fine. However, 3UK has shutdown their 2G service and solely relied on their existing 3G service. This will post a problem to users because they will experience no signals when they are at certain areas. 3UK does not recognise the problem at all. They think that they will be able to have 99.99% 3G coverage of the whole nation.
As mentioned before, Skype could be installed on most of the present mobile phones. It ranges from Symbian s60 to Android 3.1. However, I do find that there are problems while using Skype under certain conditions.
First of all, if you are using a Nokia mobile phone, most probably you are using a s60 device. With Skype installed, please do not install any third party calling apps like Nimbuzz or Truphone as it will crash both Skype and the third party app. That is in relation to Symbian s60. I have no problems with s40 mobile phone as it does not support multitasking so it will automatically exit the problem when you minimise any app. The issue is more problematic when you are using a Symbian ^3 device like the Nokia N8. It will totally crash both apps and will most probably stall the OS itself.
However, if you are using an iOS or an Android 2.1 and above, you will have no problem in using both Skype and any third party apps to make or receive calls. In fact, I have tried using Nimbuzz and Skype running side by side. I do not encounter any problems using either one of them.
In a nutshell, if you are using an s60 or a ^3 device, just install Skype or the third party app but not both. It is fine to install both on other platform.