Questions about WiFi/3G, Texting and Battery Usage

G'day. I have an iPhone 4 and would like to know the following:

1) Is 3G or WiFi necessary to receive and send texts? I find sometimes I don't received or get failed sent message notifications when these are not engaged.

2) Does it use significantly more battery to have 3G or WiFi engaged all the time? Does the phone automatically switch to WiFi when it becomes available, therefore not using the data plan (3G)?

3) Do iPhone batteries have a 'memory'? Do I need to run the battery down to the Red-line to maintain battery 'fullness'? I have been told with my MBP to plug it in whenever possible during use, but run it down about once a month to 'excercise' the battery. But batteries only have a certain number of charges.

Thanks

1) Yes...

2) Don't know - I have never turned either one of them (nor bluetooth) off since the first iPhone (over 6 years ago). Yes.
(I have gone into the wifi settings and turned off the function that continuously searches for a wifi network - then manually log in to the wifi networks I am familiar with - home, work, kids house, etc. and it will remember those and auto log you in when you are in range).

3) Personally - I don't even consider the battery. I use the phone the way I want and plug it in to charge when it needs it. Still have 2 3GS iPhones here - so 4+ years old - mine still went 1-2 days with several hours use each day - the wife's still went 3-4 days between charges when we finally retired them a couple months ago.

Thanks for the helpful responses. Anyone know from experience of reference about question #2?

You don't need 3G to send / receive texts - SMS is part of the GSM protocol. All you need is a phone signal (i.e. the same as what you need to make voice calls).

You need a data connection to use iMessage but it doesn't need to be a 3G level connection - theoretically GPRS is all you need but I tend to find it times out unless you have at least Edge.