I believe this the latest OS for the 8707
BlackBerry 8707vxxx8482; / Pkg:4.2.1.148, App:4.2.1.94, Plt:3.3.0.21 (PROXIMUS)
BlackBerry 8707gxxx8482; / Pkg:4.2.1.148, App:4.2.1.94, Plt:3.3.0.21 (PROXIMUS)
can be found from Proximus at this link:
BlackBerry Operating System Downloads - BlackBerryFAQ
Do follow the instructions posted to remove the vendor.xml file, further directions at the FAQ site.