First cell phone, LG Rumor?

[She's got me dancing]

http://anymobileanytime.sprint.com/bogo/index.php?pid=3id12=MA:LP:20090909:FREE-ACQ The link to the website. The phone I am talking about is the 2nd furthest on the left.
Hey. Now to begin honestly I know these few questions will sound incredibly stupid to most people but i'm getting my first cell and really would like to know as much as possible also i'm 14 so cut me a little slack please. Here it goes.

1. First off i'm not really understanding the whole coverage thing. If I type in my address on a coverage map on the Sprint (NYSE: S) website i'm getting a LOT of locations to show up that are all about half a mile to a mile away from my home. I understand that this is going to effect the reception but i'd like to know if it will work well but I still don't quite understand exactly how it works. (I live in Renton, Washington if this matters. I'm honestly not concerned about sharing my city name.)

2. What is a Mail-In Rebate? Because when I look at the phone offered on the website it says Buy one for $29.99 get one free! Then in small text below it states After a $50 mail-in rebate, eligible upgrade (Or new-line activation) and a two-year agreement per-line. What does this MEAN? Does it mean I have to mail in $50 as well as pay online for the phone itself? Or is this some sort of discount? Does it mean I can't activate it or begin a plan until it is mailed in?

3. If this matters i'm getting an LG Rumor from sprint. Keep in mind i'm doing this for a texting phone to easily talk with a girl i'm in a long-distance relationship with (She lives in Texas) and I don't really care much for minutes or internet access.

4. Last of all. I have about 8 friends I will be texting including the girl. So if i go with sprint the majority of them are on verizon. Will this cost me or them more if I text them if they are on a differen't provider with an unlimited texting plan will they be charged to view it or something like that? What i'm asking is will there be any downside for me or them if we all have unlimited texts and are texting eachother despite being on differen't plans?

That's about it. I would really appreciate a very solid and informative answers. I'm sorry i'm sure at least some of this sounds stupid but i'd really like to know it all. PLEASE explain well. 10 pts for best answer.
Also if anyone can reccommend me another phone that is $40 or less that they think will last longer, etc. Go ahead.