If it's connected in storage mode you should see the content mounted in '/media/Nokia N900' What does dmesg tell you after connecting USB ?
[ 2844.518017] usb 2-1.2: USB disconnect, device number 3 [ 2847.369485] usb 2-1.2: new high-speed USB device number 4 using ehci-pci [ 2847.548096] usb 2-1.2: New USB device found, idVendor=0421, idProduct=0105 [ 2847.548107] usb 2-1.2: New USB device strings: Mfr=1, Product=2, SerialNumber=5 [ 2847.548114] usb 2-1.2: Product: Nokia N900 (Update mode) [ 2847.548118] usb 2-1.2: Manufacturer: Nokia [ 2847.548123] usb 2-1.2: SerialNumber: 4D554D333737313636 [ 2848.165106] NET: Registered protocol family 35 [ 2848.183825] usbcore: registered new interface driver cdc_phonet [ 2849.274547] usb 2-1.2: USB disconnect, device number 4 [ 2855.902278] usb 2-1.2: new high-speed USB device number 5 using ehci-pci [ 2855.996984] usb 2-1.2: New USB device found, idVendor=0421, idProduct=01c7 [ 2855.996995] usb 2-1.2: New USB device strings: Mfr=1, Product=2, SerialNumber=3 [ 2855.997001] usb 2-1.2: Product: N900 (Storage Mode) [ 2855.997006] usb 2-1.2: Manufacturer: Nokia [ 2855.997010] usb 2-1.2: SerialNumber: 372041756775 [ 2855.998288] usb-storage 2-1.2:1.0: USB Mass Storage device detected [ 2855.998716] scsi7 : usb-storage 2-1.2:1.0 [ 2857.000122] scsi 7:0:0:0: Direct-Access Nokia N900 031 PQ: 0 ANSI: 2 [ 2857.000819] scsi 7:0:0:1: Direct-Access Nokia N900 031 PQ: 0 ANSI: 2 [ 2857.001598] sd 7:0:0:0: Attached scsi generic sg2 type 0 [ 2857.002201] sd 7:0:0:1: Attached scsi generic sg3 type 0 [ 2857.013112] sd 7:0:0:0: [sdb] Attached SCSI removable disk [ 2857.015976] sd 7:0:0:1: [sdc] Attached SCSI removable disk [ 2863.415351] usb 2-1.2: USB disconnect, device number 5 [ 2873.652698] [UFW BLOCK] IN=wlan0 OUT= MAC=01:00:5e:00:00:01:c0:c1:c0:1e:9a:b0:08:00 SRC=192.168.1.1 DST=224.0.0.1 LEN=28 TOS=0x00 PREC=0x00 TTL=1 ID=0 DF PROTO=2 [ 2874.267446] [UFW BLOCK] IN=wlan0 OUT= MAC=01:00:5e:00:00:fb:c0:c1:c0:1e:9a:b0:08:00 SRC=192.168.1.1 DST=224.0.0.251 LEN=32 TOS=0x00 PREC=0x00 TTL=1 ID=0 DF PROTO=2 [ 2999.777682] [UFW BLOCK] IN=wlan0 OUT= MAC=01:00:5e:00:00:01:c0:c1:c0:1e:9a:b0:08:00 SRC=192.168.1.1 DST=224.0.0.1 LEN=28 TOS=0x00 PREC=0x00 TTL=1 ID=0 DF PROTO=2 [ 3003.876076] [UFW BLOCK] IN=wlan0 OUT= MAC=01:00:5e:00:00:fb:c0:c1:c0:1e:9a:b0:08:00 SRC=192.168.1.1 DST=224.0.0.251 LEN=32 TOS=0x00 PREC=0x00 TTL=1 ID=0 DF PROTO=2 [ 3050.106003] usb 2-1.2: new high-speed USB device number 6 using ehci-pci [ 3050.199459] usb 2-1.2: unable to get BOS descriptor [ 3050.201191] usb 2-1.2: New USB device found, idVendor=0421, idProduct=0106 [ 3050.201203] usb 2-1.2: New USB device strings: Mfr=34, Product=38, SerialNumber=0 [ 3050.201209] usb 2-1.2: Product: Nokia USB ROM [ 3050.201213] usb 2-1.2: Manufacturer: Nokia [ 3050.513211] usb 2-1.2: USB disconnect, device number 6 [ 3050.990494] usb 2-1.2: new high-speed USB device number 7 using ehci-pci [ 3051.168891] usb 2-1.2: New USB device found, idVendor=0421, idProduct=0105 [ 3051.168902] usb 2-1.2: New USB device strings: Mfr=1, Product=2, SerialNumber=5 [ 3051.168908] usb 2-1.2: Product: Nokia N900 (Update mode) [ 3051.168913] usb 2-1.2: Manufacturer: Nokia [ 3051.168917] usb 2-1.2: SerialNumber: 4D554D333737313636 [ 3052.074767] usb 2-1.2: USB disconnect, device number 7 [ 3125.800354] [UFW BLOCK] IN=wlan0 OUT= MAC=01:00:5e:00:00:01:c0:c1:c0:1e:9a:b0:08:00 SRC=192.168.1.1 DST=224.0.0.1 LEN=28 TOS=0x00 PREC=0x00 TTL=1 ID=0 DF PROTO=2 [ 3133.074754] [UFW BLOCK] IN=wlan0 OUT= MAC=01:00:5e:00:00:fb:c0:c1:c0:1e:9a:b0:08:00 SRC=192.168.1.1 DST=224.0.0.251 LEN=32 TOS=0x00 PREC=0x00 TTL=1 ID=0 DF PROTO=2