I just bought an Iphone3g and was wondering if I could use the usb cable from my Sansa 4.0 to connect my phone to my computer without frying it?
I don’t know what a “Sansa 4.0” is (there are many models of Sansa players, and most of them come in 4GB capacity if that’s what you meant), but generally the answer is “no”. If the cable has a proprietary Sansa connector, it’s not safe to use with iGadgets. The connector may look the same (and it may even fit with just a little extra effort), but the power is on different pins and will fry your fruity player.
ABSOLUTELY NOT!!!
Come hither, said the spider to the fly…
Don’t use the Sansa cable on that iPhone, it won’t work. The biggest danger is in the reverse, as the iPod dock connection includes 12 volt “firewire” power. Connected to a PC USB port, all we have available is 5 volts.
Plopping a Sansa into an iPod dock can most certainly damage the device. The iPhone connection can easily be damaged, and repairs for all things Apple are very expensive, so don’t try to weasel the iPhone onto the Sansa plug!
So far, I’ve seen two shattered fourth generation iPhones, with a glass “kit” costing about two hundred dollars. Nuts. A complete HTC device costs less than that, hehe.
Bob 
Thanks for the information, everyone. The guy that sold me the phone at the AT&T store kept my usb cable and now I can’t get him to return my calls. I have a Sansa and thought the USB from it might work but wanted to ask some people who actually know what they’re talking about before I tried it.
Thanks again!
Might be time for a little nose-to-nose time. May not take much to get it back out of him … may take an appeal to his higher-up. Make take an appeal to his sense of fair play vis-a-vis the cost of a USB cable v. the cost of a paint job for his car. Properly approached, most people will listen to reason. 
