We use QB online...can spit out an estimate or an invoice from my phone directly to customers inbox in minutes, plus our accountant can log in and pull reports for tax purposes.
Every service here is free:
Google Drive (Free spreadsheets, docs in the cloud)
Google Voice (speech-to-text voicemail, plus in the cloud)
Use Contact Form 7 to send proposals (backlinked on our website, password protected, wordpress required)
WhoReadMe.com (know when someone opened an email)