Email, Contacts and Calendar

[#1]

Could PN enhance its Email service by including calendar and contact synchronisation for desktops and mobile devices?
There are a number of service providers doing this, and there is increasing popularity of mobile devices that can be used with such a service.
Looking at Mobile Me by Apple (which also includes file storage) there is a bit of a gap for PN customers in that they only offer 5 mailboxes on the family account. Also, I'm not sure if you can use your own domain. (I'm told that you can.... but I've found no refernece yet)
That said this household is considering such a move for the utility it provides.
I don't expect this enhancement for free. Implemented well with secure reliable storage it would be worth an extra monthly charge.
Could you do it for <£5pm?

[#2]

Hi,
If there was an open source (or even viable commercial product) that offered this functionality, it's something I could take a look at us running for customers. If anyone has suggestions they should shout up.
As it is though I don't think we could be effective at developing something like this ourselves from scratch - it's not really what we are expert in. That means it wouldn't be as good as something developed by people who were dedicated to the project full time, and who had a few years to make it really good (Not a luxury available to our developers at the moment).
We did look at Zimbra in the recent past, but this was deemed to be a bad fit for our network architecture in the end, and the testing of it we did highlighted some major issues we could not easily have got round. As it is, we've decided on Roundcube as our next webmail software. That won't do Calendar stuff though, although frankly I don't think anyone will better the Google Calender product for functionality or value for money any time soon.
Ian

[#3]

I don't know what you class as 'viable'. Presumably you have ruled out MS Exchange?
I can't offer experience. I only know that services and server products to deliver them are available. Mailsite, Kerio.... Are you considering a service customers might pay for? Not just an enhancment to the 'free' service?
As for Google, who knows what its really worth to Google. Like many I'm wary about having my life indexed by others for their own business purposes.