These are excellent questions, but I think I would add a slightly more general question:
Can you show us an example of what one of these would look like? Like, create something that looks like like it would look, even if the actual numbers themselves aren’t real. (That being said: the closer your example document is to the actual thing you need, the easier it will be for us to help.)
(Here let me pause to reiterate and affirm what @sylumer said: telling us what format the file really needs to be in for the end product will help show us what we can use. It it has to be an excel sheet, that’s one thing. If it has to be a PDF, that’s another. If it just has to be numbers in a table printed out on a piece of paper, that’s different.)
I presume that each month is different and you have to fill-in some values (presumably based on how much you used your cell phone for company business)?
Do you have that information in some form already, and just need to enter it into some kind of table?
Are you trying to do this on a 1) Mac, 2) an iOS device, or 3) either?
ps - in the meantime, if you have an iPhone, get Due and put a reminder on the 1st of every month that will remind you to do this and have it repeat until you do it… even if you aren’t automating it. Then check it off and it will remind you the following month. Due is super-useful for nagging yourself into doing things. If it reminds you to do this just once, it will basically pay for itself.