Hi,
A 3845 or even a 3825 will surely do what you need. There is a feature called "CCME" by which the IP phones, cisco or other brand, will work like a feature-rich PBX without additional components. In the branch offices you can use smaller router like the 2801 with the same CCME feature.
For the switches, the smaller model that cisco makes, with PoE support is the CE-500, unfortunately these switches don't enjoy much of a reputation among professionals.
The 2960 models are only layer 2 switches, this is not a problem in itself, but they have no POE that is very important in IP telephony to eliminate the ugly power bricks that are so cluttering for the desk.
The next models that supports PoWE are the 3560, then the 3750 that is stackable with an highspeed backbone. There is also a version of the 3750 with 48 ports and PoE that fits inside the router in case you like a super-integrated solution.
The wireless part should be discussed separately because it's a matter in itself, but for starting you can put a wireless module in the router itself and if it not too buried in the building will start with some coverage already.
The most important thing is that you locate a cisco partner that is honest and straightforward in making the design with you. Then if you have questions you can always come back in this forum.
Hope this helps, please rate post if it does!
