Hello Maria,
Freescale does have a transceiver that supports full RX/TX functionality in the sub-GHz space (290-340 MHz, 424-510 MHz, and 862-1020 MHz frequency bands):
KW0x |Kinetis KW0x Sub-1 GHz Radio MCUs|Freescale
In addition there is an application note in its final stages using the MKW01 as the receiver for the FXTH870xD TPMS Sensor which I can forward to you when it completed. Please send me an email directly at frank.latona@freescale.com for this.
Thank you for interest in Freescale TPMS Solutions.
Frank