I am doing my research also ...used to have a Sony Ericson that would never pick up Orange in La Romana or Higuey , now have a Samsung S5 which does not pick up Orange in many places . I am trying to change over to Claro with the same number as several of my friends get three bars with Claro where I only get one or nil . And I am going to try with an apple . Funny thing is that my Samsung tablet picks up two bars more than my Samsung cell phone in many places...can someone explain ???
S5 has three different versions, depending on where you bought it it may or may nto support Orange on 3G+ (HSDPA) but will support it on 2G (GSM/EDGE data).
HSDPA 850 / 900 / 1900 / 2100 - G900F, G900I
HSDPA 850 / 1900 / 2100 - G900A
HSDPA 850 / 900 / 1700 / 1900 / 2100 - G900M
HSDPA 850 / 1700 / 1900 / 2100 - G900T
Orange uses 900 MHz.
You can usually find your exact model under the battery.
If your model supports Orange, then to get a better signal on Orange, flash a different radio file
Extract the radio file from Lollipop ROM and flash it over with Odin, you can flash it over even Kitkat or older Android if you have.
You can download the ROMs here
e.g. for G900I
http://samsung-updates.com/device/?id=SM-G900I