Multimedia applications are driving wireless operators to add high-speed data services such as E-GPRS, UMTS and WLAN (IEEE 802.11a,b,g) to the existing GSM network. This creates the need for multi-mode handsets that support a wide range of standards with different RF frequencies, signal bandwidth, modulation schemes, etc. This generates design challenges for the building blocks of the physical layer. In addition to the above protocols, mobile devices often include Bluetooth, GPS, FM-radio and TV services that can work concurrently with data and voice. Sharing and/or switching transceiver building blocks in these handsets is used to extend battery life and/or reduce cost. More specifically adaptive circuits that can reconfigure themselves within the handover time are used to enable a single receiver/transmitter covering all the different standards while ensuring seamless interoperability. This paper presents RF and analog base-band circuits that are able to support GSM (with Edge), WCDMA (UMTS), WLAN and Bluetooth using reconfigurable building blocks. The blocks can trade off power consumption for performance on the fly, depending on the standard to be supported and the required Quality of Service. Experimental measurements in a 0.13 um CMOS technology are presented and discussed.