Most HTC phones are able to detect which mobile operator you're using based on the SIM card you inserted, and then use the preset Access Point Name (APN) to connect to your mobile operator's data network. 
	 You can add a new (APN) when roaming or if you have difficulty establishing a data connection. 
	 
 
  
 
	 -  
		 With two fingers, swipe down from the status bar to open 
		  Quick Settings. 
		
-  
		If 
		  Mobile data is off, tap the 
		  Mobile data tile to turn it on. 
		
-  
		Tap  to open the 
		  Mobile network settings screen. to open the 
		  Mobile network settings screen.
-  
		Tap 
		  Access point names. 
		 
		If your phone has two SIM card slots, select a slot first, and then tap 
		  Access point names. 
		
-  
		On the 
		  APNs screen, tap 
		   and enter the APN settings. 
		
-  
		 Tap 
		   and then select the new APN on the 
		  APNs screen. 
		
 
		 
		  Note:  
			  Some mobile operators may not allow you to change the predefined APN or add new ones.