Well some phones let you mount the phone (well, actually the memory card usually) just like you would mount any mass storage media: plug the USB cable in, possibly select from the phone that the connection is to be a "data transfer" or "mass storage", and the icon should pop on your desktop if you have dbus/hal letting you move data in and out.
If your phone doesn't support that..well, the next best option is probably Bluetooth if it's available. Slow as what, but nowadays the Linux Bluetooth support makes it more or less easy.
So, if you can, mount the phone memory as mass storage and access it like you would access a USB stick. If you can't do that - the phone doesn't do it for example, but instead wants a special program to access it - then you have to obtain a piece of software that knows how to work with your phone specifically. Gnokii works for some Nokia models, but I didn't have luck with it; Wammu did connect my phone trough USB cable, and actually transfer messages and address book entries to and from the phone (=> it was able to connect to the phone internal memory, not just the memory card), but it failed with moving calendar entries, so it was pretty much useless. I take it the phone model just wasn't supported well enough, or then the phone software was not new enough, or something. Wammu offers several kinds of connection types trough Bluetooth or USB cable (or datacable?), so it might be a good bet for you. But if you just transfer music or such to and from the memory card, stick to the mass storage method - it's faster and easier.