[Q] droid 4, GSM? topic

I recently purchased a droid 4 and it is unlocked and rooted. ive been to Verizon and they said I could not use a gsm carrier even tho it has gsm and global along with cdma option. I was just wondering if theyre putting me on or if theres another way around it. any info would be greatly appreciated. ive heard of flashing bionic and it might work. thanks ereone.