You can already do a Xero to Xero invoice. I would like to link in to other on-line invoice aggregator services via their API and send an invoice to them electronically. I have a couple of multi national clients who refuse to accept invoices that are emailed with PDF attachments. They want me to use their invoice aggregator which either costs me money (if I integrate using their API) or time if I log on to their portal and manually enter each invoice (yeah right!).