Considering all the issues with different phone loads and the likes the only reasonable suggestion can be to use physical phones. There's an old piece of software that emulates the 7960 (don't recall the name but if you search old posts you should find it), and as far as the 70 goes, the IP Communicator is a close equivalent. Still, it could be fatal if you use software phones to test an application that your client is going to use on hardphone.. make sure you plan on plenty of testing on real phones.. there's simply no alternative.
If you're not working for a Cisco Partner, get in touch with one.. they can sell you an IPC (there's no demo licenses and you need a call manager anyway). Compared to the phones, it's quite reasonably priced. I'm not sure if they have a program to get hardware for a reduced price for development purposes (there's one for partners.. but it's forbidden to resell hardware acquired under this program to anyone). But be aware that while the IPC is a good testbed to incept your applications, you have to switch to hardphones at some point. I use the IPC quite often on the road, at home and a customer sites, but it doesn't always act the same as a hardphone.
I'm not able to access my old voice mail messages all of a sudden. The recording says something like 'the message is currently not available'. This has never happened before in all the years I have been using this system. I have t...