Can I put a Straight Talk of Tracfone sim card into an iPhone?

Currently I have an LG 800G through Tracfone. I want to buy an iPhone 4S or 5 off of Amazon or Ebay as an upgrade. I want to stay on Tracfone, but I could switch to Straight Talk if I had to. I have a lot of questions. Could you please answer as many as you can?

Can I put a sim card into an iPhone?
Does the iPhone that I buy have to be through a specific carrier?
Does the phone have to be unlocked for me to do this?
Do I have to buy the $45 Straight Talk plan? After, can I buy the $30 plan?
If I can stay with Tracfone, do I have to buy a specific amount of minutes?
Will I be able to get data, texts, calls, apps, etc. When I switch?

Sorry that this is very long. I really need to know because I want to do this for my birthday, which is in a few months. Please answer as many questions as you can, but I will appreciate it if you can answer them all.

Can I put a sim card into an iPhone? Depends which iPhone, it'd have to be an unlocked iPhone but you wouldn't be able to use a Tracfone sim - their sim cards are locked to that phone and that phone only. It's company policy.
Does the iPhone that I buy have to be through a specific carrier? It should be unlocked. However, if you buy a sim on Straight Talk's website (you can't buy a phone and take the sim out of it - again it's locked to that phone) and the website says it's a T-Mobile Compatible Sim, you can get a T-Mobile iPhone, but only a T-Mobile iPhone or an unlocked iPhone.
Does the phone have to be unlocked for me to do this? Answered up there ^ :P
Do I have to buy the $45 Straight Talk plan? After, can I buy the $30 plan? I think you have to be on the $45 one, I think they discontinued the $30 one. You can get the $60 one but the difference with that one is international calling.
If I can stay with Tracfone, do I have to buy a specific amount of minutes? You can't stay with Tracfone.
Will I be able to get data, texts, calls, apps, etc. When I switch? Yes, you'd be able to do this with the Straight Talk Sim card. To get a Straight Talk sim, go on their website and mouse over the word "Phones" then click on "Sim Cards".

You can put a sim card into an iPhone.
The Iphone should be unlocked in order to use it with any GSM sim card.
You should buy the iphone from a GSM network carrier, like Straight Talk of Tracfone, in order to be possible to unlock it to work in any GSM network. The Iphone 5 is a dual GSM CDMA phone, you can use it with any GSM network if it is unlocked. Both Iphone 4S and Iphone 5 can be unlocked to work with GSM sim Cards. CDMA phone can't be unlocked to work in GSM networks.
You also can unlock your LG to work with both Straight Talk of Tracfone sim card.