At&t and t mobile are both gsm phones and can use eachothers towers depending on where you are if you're in an area where they have an agreement to "share" then yes Verizon and sprint are cdma and if they have an agreement then yes they can share but bonus if you have a cdma phone with an active sim cars like (4g LTE) you may be able rouse a Sprint or Verizon 4G LTE phone on a gsm network if roaming data is turned on and there is an agreement in the area) basically its really complicated when it comes to sharing towers best thing you can do is call your carrier and ask if there is roaming or normal coverage in the area only