Aetna Inc. is becoming the first health insurer to team with Microsoft Corp. to give its customers an Internet-based vault for storing medical records they can access even if they change jobs or leave their health plan. Aetna will allow some customers to transfer electronic personal health records to Microsoft's HealthVault, a platform that lets providers look at the information if they have patient permission. The vault will give the insurer's customers continuous access to their claims information and anything the patient wants to add, like clinical data or past medical records, said Aetna representatives.