应该是不能在美国境内放弃绿卡的（除非在海关或已经用非移民身份入境了）

I-407 instructiions说：

“Form I-407 is used by lawful permanent residents who are outside the United States or at a port of entry who want
to abandon their LPR status. Form I-407 may also be used by individuals who were admitted into the United States as
nonimmigrants or paroled into the United States after abandoning a prior LPR status, and who now want to record that prior
abandonment of LPR status.”