Well, since people aren't giving you a quality answer explaining everything; i'll go ahead and tell you everything that needs to be set up in order to go online starting from 3.55 OFW.
Firstly you're going to have to install a Custom Firmware of your choice. Keep in mind that there are multiple Custom Firmware's and you should take your time to make sure this is the one you want. Also be sure that the Custom Firmware you'd like has a current Spoofer for 4.60. If it doesn't, you will NOT be able to go online.
Secondly, you're going to have to install a 4.60 Spoofer to your corresponding Custom Firmware so that your system spoofs to the system update version 4.60. This will engage you for online play because as you know, you can't go online to PSN unless you are on the most current version.
That just about sums it up, install a Custom Firmware then spoof your console.
Personally, i'd recommend going to Rebug 4.46 or going to PS3ITA 4.50 - 4.55