Serious question about reservation or booking plugins

Hello people,

First i have to say i don’t mind paying for a PRO version of a simple plugin if i can get the best product. I don’t want an I can do everything kinda plugin, it just has to do what it says it should do.

I have this one huge client in my portfolio based on friendship not on my development skills but i like to keep this client because it’s family. 🙂

The company info:
– 223 Employees (plumbers -working people)
– 95.000+ Clients and growing fast last 2 years.
– Around 15 Office people doing all the boring stuff.

At this time the company is still driven by Grandpa’s philosophy doing everything by paper and hand (scrapbook). This means calling all clients daily to make an appointment, write them in a book and make a working plan for the next day(s) for all employees. All done on 3 computers with 15 people 🙁

It still works perfect but while the company is growing year after year the space to make an error is very limited by now so this is why i thought it would be nice if i could upgrade the company to make it a bit more 2012. More will be done with computers and if i could fined a way to reduce the number of calling hours it would be great.

Options i would like to see.
– Clients info’s, all in the Database so we can sent out a reminder Email instead of calling them. (just simple Newsletter script – easy )

– People click on the LINK inside the Email to visit the schedule page where they can pick a date and time and push apply.

– Back-end, we get an Email notify that there has been one bookmarked and we can approve it. -> Email back to this client of course that we have accepted it.
– Multiple people can mark the same date and time because we have more then one employee in different region’s. Not looking for Hotel Room reservation where the date is auto. selected by someone else because there has been one booking at this date,

Maybe a few functions more would be great but there is only one thing that matters most!
IT HAS TO WORK.

I can’t sell half working Open Source scripts that’s why i’m asking people only to submit the best plugins out there.
The website is redesigned and transferred from Joomla to WP 2 years ago by me and they keep everything up-to-date they seriously love how easy WP works and still talk very highly of me because i made the switch from Joomla to WP for them look easy.

Could somebody with more experience maybe point me into the right direction?
Thanks already!