Can't you submit transaction before it syncs as long as you you're confident the transaction will be valid? For a business, they could maintain a current sync and you submit your transmitting address to them and they can verify, that way your smartphone doesn't have to get bogged down with the task of anything other than signing the transaction.
If I recall, the standard Bitcoin client doesn't work until the blockchain is synced. I've had to wait an hour to do a transaction I wanted to do because I hadn't opened it in a few months.
