Long range wireless communication between two arduinos?
Your range of options depends strongly on what your budget is, what country you are in, whether you are a licensed radio operator, whether cell service is available, etc.

If you aren't licensed:

In the USA, unlicensed (or lightly licensed) radio options include GMRS (General Mobile Radio Service), FRS (Family Radio Service) and CB (Citizens band radio).  GMRS and FRS range typically is at most a few miles – ten miles is too much to hope for.  CB range would be ok but CB radios often are fairly large and antennas would be large, eg nine feet long.  I don't know whether it is legal to transmit digital data over GMRS/FRS/CB radio.  

If you are licensed:

2-meter band radio might be a good choice.  Frequencies are 144 MHz to 148 MHz in the Americas and Asia, or 144 MHz to 146 MHz elsewhere.  Per wikipedia, 


  The license privileges of amateur radio operators include the use of frequencies within this band  for telecommunication, usually conducted locally within a range of about 100 miles (160 km).


If cell service is available:

Consider a GSM shield, eg the Arduino GSM Shield.

To access the cell network you would need to buy a SIM card for each GSM shield.

GPRS (General Packet Radio Service) on GSM provides data rates between 10 and 240 kbs.  Other GSM protocols may be faster or slower.  Data rates depend also on whether 3G service is available or only 2G.