If you’re looking forward to the possibility of flip-flopping your smartphone’s SIM card between a Verizon Wireless 4G phone and an AT&T 4G phone, we have some bad news for you. Verizon Wireless spokeswoman Brenda Raney confirmed to PCMag on Friday that the carrier’s 4G LTE phones will not be compatible with AT&T’s 4G LTE network because the phones “run on different frequencies.” PCMag explained that while the two carriers operate within the 700MHz frequency band, AT&T will operate mostly within the 704-746MHz bands while Verizon’s 4G LTE will utilize the 746-787MHz frequencies. Additionally, Verizon still routes its voice calls over its 2G/3G CDMA network while AT&T uses GSM/HSPA. That means, until both networks are fully utilizing voice-over-LTE, it just won’t work. Sascha Segan, the article’s author, notes that it is possible for phone vendors to create devices that operate with the frequencies used by both AT&T and Verizon Wireless, but it would likely require the carriers to ink out some sort of agreement first.