iphone booking app for utility company

Need to develop an iphone/ipad app for a natural gas plumbing company, so their construction company clients can book appointments for work. The clients need to book a date and location of work, and the type of work required from three job type options. The booking application just generates an email to the booking email address of the company and they will check this before sending back an SMS or email confirmation. User will need to have account and login details (can be stored after initial log in), to execute booking request. The first login needs to generate an account application which the company can approve or decline to avoid spammers.