In many cases yes. Optus have a service called international roaming which allows customers to continue to use their Optus mobile phone overseas. For more information on this service please visit the Optus website at http://personal.optus.com.au/web/ocaportal.portal?_nfpb=true&_pageLabel=Template_woRHS&FP=/personal/mobile/usingyourmobileoverseas/prepaidautoroam&site=personal