I use the ol aluminum invoice tablet. Get the signature of the customer that they received the goods and services satisfactorily. Then at the end of the week transfer to Quickbooks. I like a good old fashioned signature. The electronics are nice but not binding in court, and it lets me put caveats onto my invoices.
The best thing I have done lately is get the intuit payment2go credit card acceptance app for my phone. The goal here is to get the money.
I look at a service call as a multi stage aproach; sale, contract, performance, completion. The bookkeeping is an office detail which needs scrutiny on the price, where the overhead is, paying the bills and taxes etc.
Two different tasks altogether.
That 5 minutes of talking to the customer after the job completion is keeping that person as a customer for life. Giving them something tangible after the sale reminds them of your valuable service. A paperless app is fast but sometimes fast isn't what you need or want. You paid for the advertising to get there, you have a real life customer in front of you, take advantage of that. If you want to spend your money on something get neon glow in the dark stickers to put in there panels. Thats were they go when the lights are out and there computer and routers shut down.