The iPhone 4S will arrive at retail stores across South Florida on Friday. If you plan on picking one up, you should have a purchasing battle plan in place.

The latest iPhone will go on sale at carrier stores – AT&T, Sprint, Verizon – as well as at retail stores – Best Buy, Target, Radio Shack and Sam’s Club.

If you simply must have one on the first day, here are tips to help that happen:

Expect long lines. No one knows for sure whether they will emerge, but they certainly have across South Florida during previous iPhone releases. And some stores will open early. For instance, AT&T stores will be open an hour early – by 8 a.m. Call your local store today to get details.

Consider trading your old phone: For instance, Target is offering up to $200 in credit for an iPhone 4, and up to $120 for an iPhone 3GS.

Stick to your budget: Prices range from $199 for the 16GB model to $399 for the  64GB version, plus the cost of a two-year contract. Don’t spend more for more memory if you don’t download lots of videos and photos onto your phone. And make sure you consider the costs for extras, such as car chargers, cases and display screens.

Don’t feel pressure at the cash register: Don’t buy the most expensive phone because others near you are doing so. And don’t buy the 8GB phone because the other models have run out. It will be worth the wait to order the phone you really want and wait to get it later.

Skip the 4S: Yes, it may be the best iPhone out there, but if you are moving up from a dumb-phone you will be amazed at what the iPhone 4 (available for $99) will do for you, or even the 3GS, which Apple and other retailers are offering for free with a two-year contract. Those are major deals considering all of the features you will get.

Save your contact information: Before you trade-in, make sure to download all contacts so you won’t have to worry about losing them when you hand your old phone over. Carrier stores may help with this process, but it could slow things down. And mistakes happen. Be safe, do it yourself, even if you must write contact information down with a dreaded pen or pencil.

Be comfortable: Wear comfortable clothes in case you will be in line long. Bring water and snacks.

Bring a buddy: It will help the time go by faster if you have a friend. And if there are long lines, you can take turns keeping a place in line while one or the other takes bathroom breaks or makes a food run.