Driftwood is awesome. It's beautiful, lived a full life as a part of a wooded eco-system, an oceanic eco-system, and a shoreline eco-system. And can make for some very lovely art.
Step 1 is pretty obvious. Collect wood. Make sure you're collecting wood from a beach or shoreline that allows wood/artifact collection. Many state/national shorelines are protected.
Look for wood that has smooth edges and aesthetically pleasing. Wood that has been part of a fire can be challenging to work with but a little burn is OK. I tend to go for pieces that are under 2 feet in length and have a good amount depth (3-5 inches) at it's thickest point.
Step 1: Clean That Wood, Yo!
I like to give it a nice long bath. 24 hours in a 1:8 vinegar/water solution. More potent if you feel like it. Halfway through this process I'll get in there with a good old toothbrush and brush off excess sand, dirt, crust, demons, control issues, etc. Then let it soak a bit more. After 24 hours, take them out of their spa treatment and give them a wash in clean water (hose works, or shower with them if you're a little bit of a perv like me).
Rinsed? Rad. Now it's time to bake. Oven goes to lowest setting. For me it's about 250 f. I put my wood on the middle rack in my hot oven and STAY HOME for the next several hours. Why do I stay home? Mostly paranoia that I'm going to burn my house down. But really it's so I can rotate the wood and give my friends an excuse for not going out. Baking time depends on the size of the wood but you want it to get totally dried out. The vinegar should kill all the gnarly stuff and the baking will kill the zombies.
Step 2: Sand, Drill, Add Hardware.
POWER TOOL TIME, Y'ALL!
But first sand down the wood to keep it smooth. The ocean did a great job of this for you, but clean up any little rough spots with a fine grain sand and some elbow grease.
Set your piece down. How does it sit? Figure out where the piece naturally wants to sit and then decide where the front and back are going to be. For my piece above, I loved the upper ledge but the weight of the phone up there would have toppled the piece so keep in mind the final use.
If your piece looks like mine, where you can't drill straight down and out try a 1/4" bit and drill about 3/4 in down then from the back, drill in towards your initial hole.
Feed your iphone cable into the wood from the rear. Use a wood glue to fill the top hole with and with a piece of tape (or your finger and some spare time) hold the dock end so the glue dries it into place. I keep about an 1/8" of space between the glue and the top of the wood surface. Once the glue has stiffened (even if not dry) Fill in the rest of the way up with a mix of half water and half wood glue mixed with saw dust from your drilling adventure. This will mimic the look of the surrounding wood and give you a really clean natural look. See photos above.
Step 3: Make Your Friends Jealous
Plug the phone in and attach your usb end to a wall socket. Boom. You're fancy now.