SAP (Sim Access Protocol) will give you text messages because the Bluetooth kit becomes the phone, whilst all the radio except bluetooth are disabled on your handset. Bluetooth is used as a protocol for the car BT kit to gain access to your phones Sim card. Generally speaking this also gives the best signal quality since the car will be using its own aerial for calls etc.
The other mode is HFP (Hands Free Protocol), in this mode the BT kit becomes a giant handsfree kit, since the phones radio is still active, the handset receives the text messages. This setting results in lower signal strength usually, because the phone handset is still using its own aerial and depending on where its located in the car and the glass used in the car, the signal could be a lot worse.
For example, when I had a previous car with SAP kit, a work colleague was unable to make a call on her Nokia phone. I had the exact same phone, but paired to the SAP kit and had almost full signal strength.
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Manny
2004 A4 1.8T Sport Cabriolet, 89K Miles
Past
2004 D3 A8 3.7 Quattro, Xenon, Bose, Blinds, Solar Sunroof, TV, ACC, phone and almost every option. 168K miles rising slowly
with retrofit AMI and DVB-T in place of Analogue
2003 Volvo S60 D5 SE Manual, 197K miles.
2001 D2 A8 3.7 QS, Bi-Xenon, Bose, Blinds, Electric Everything, retrofitted RNS-D, 191K Miles
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