The Wilson 801865 Amplifier for Verizon 4G LTE listed previously is not what you need since that only boosts LTE signals on Verizon and voice calls don't go over LTE. It would only help with data and only in locations that have LTE service.
Your idea of using a window mount to keep the installation easy is a good one. The only stipulations are that your windows shouldn't be tinted, and you need at least 15 to 20 feet between the window antenna and the inside antenna the rebroadcasts the signal in order to avoid feedback between the two. Also, this setup would only work if you can place your phone next to the window and get at least one bar of signal.
For the window setup, I would recommend a
Wilson SignalBoost DT or a
YX540 both of which have window mount options.
The
Wilson Sleek 4G-V for Verizon mentioned previously would be the cheapest option and the antenna can be mounted on the window if you get the
home accessory kit. These work really well, but the phone has to stay in the cradle so you'd have to use a bluetooth headset. It only supports one phone at a time so if you need more than one, you're out of luck. It's also the only system available right now that I can both 3G and 4G in one unit.
A system with an antenna that is outside the vehicle will always work better than a window mount option so if you want a slightly better system, the
Wilson RV and Ambulance Repeater Kit (841295) is really good. Unfortunately, the antenna that comes with it requires that you drill through the roof and mount it permanently which may not be what you want. In that case, call their customer service and they can put together a kit with a threaded antenna that you can mount to either an existing threaded mount, or to an adapter that clamps on to the ladder in the rear.
I hope that helps. Let us know what you end up going with and how it works!