LTE is slowly being introduced but it won't be fully integrated nationwide for years. For example, it took almost 3-4 years for At&t to introduce 3G in my local area after the technology was first made available and there are still huge gaps nationwide lacking 3G nationwide. Even Sprint's new 4G network is only available in a few markets currently and they only sell 1 phone that supports it.

If you need or want a new phone now, get it.