如何处理来自httpclient的数据

I'm working on a new Windows Phone 8 app. I'm connecting to a webservice which returns valid json data. I'm using longlistselector to display the data. This works fine when i'm using the string json in GetAccountList(); but when receiving data from the DataServices class i'm getting the error "Cannot implicitly convert type 'System.Threading.Tasks.Task'to string". Don't know what goes wrong. Any help is welcome. Thanks!I'm working on a new Windows Phone 8 app. I'm c