Send data to web service from a arduino+GPS+GSM

Hello.

I'm developing a vehicle tracking system and one of the ways I can do this is with a arduino that gets the coordinates of the vehicle and sends it to a server through 3G with the GSM module.

I already have the server working with a SOAP web service, this was intended to work with a smartphone as gps tracker but now we want to try it with the arduino.
My question is: Based on your experience, which are the best ways to send coordinates to the server using GSM and web services? or I have to change something in the server?

I haven't decided which modules to get so you can suggest which are the appropiate

Thanks

which are the best ways to send coordinates to the server using GSM and web services?

The best way is to send the data in the format that the web service expects it.

or I have to change something in the server?

What server? You have said nothing about the server or the service. How are we to know if you need to change something?