Yes they will work in the USA. What you want to look for is a phone that is unlocked and has all the software on it that your phone company will need.
Yes, mobile spy software could work for most of the mobile.
Cell phone tracking software can ONLY be downloaded from or onto the INITIAL cell phone, they cannot be downloaded somewhere else. This software can be found on many websites, and the Apple app store has many versions. There is no real proof as to whether any of them work, so beware of what you download.
No - usually the mobile networks will do all the 'hard work' for you.
Cell phone applications work much like the software on any other computer. They are designed for a specific operation system and use the processor to perform various tasks.
No it wont you need to get the Verizon cell phone unlocked for the T-mobile chip to work. Look on the Internet as to how to do this.
Cell phone gps tracking software is software that trilaterates (or triangulates) your location using 3 satellites in space. You can track someone yourself, if they have gps on their phone, using trilateration.
When you buy a cell phone there is always a manual that comes with it read it and it will tell you everything you need to know about it.
No you do not need a special cell phone. SMS text is a basic vertion that almost all cell phone are manfactured useing. For sms text not to work you would have to be useing a cell phone from the early 90's
Cell phone batteries are the power behind your phone. In order for the electronics to work, to broadcast a signal and to receive one you need to have power.
Most cell phone spy software is installed on phones and NOT computers. So unless you are talking about the iPad you must be referring to the iPhone. Yes, you can use cell phone spy software on the iPhone, but you must jail break the iPhone first. Sites Used To Answer This Question http://spybubblefree.co/spybubble-free-download-for-the-iphone-really/
Some apps that you can download will mask your cell phone signal. They are not completely assured to work, especially against law enforcement or some other governmental entity.