If memory serves, the 4220 is either a .Net or CE device. Version 7.0 of the RFSDK will support these devices via a TelNet client that is capable of Line Mode. WaveLink has developed several TelNet client emulators, and I have had success using them in the past on several Symbol and PSC terminals,however, you may wish to confirm that the Line Mode and VT Telnet emulation is available in some fashion(WaveLink or otherwise). If so, then the RFSDK 7.x will be capable of supporting it.