Can't connect Samsung Galaxy S2 Plus to Kubuntu

[fairy._.queen]

Hi all!

I'm trying to browse my smartphone (Samsung Galaxy s2 Plus) with Kubuntu - I really would like to avoid Windows, if possible.
However, I have tried 3 different ways and it didn't work:
1) Simply connecting the device to the pc and browsing it with Dolphin
2) Trying go-mtpfs
3) Trying mtpfs

I know some would suggest to tap on "connect as USB mass storage" on the phone, but the kernel has recently changed and I can't find the option anymore.
Can anybody help?
Thanks in advance!

[lukeiamyourfather]

Not sure about the Galaxy S2 but my Galaxy Nexus will only connect if the device is unlocked. After a few minutes of being idle it will lock itself like it's supposed to but that also causes it to disconnect from the computer.