Bluetooth carkits come in three main categories: those with bluetooth HSP , those with bluetooth HFP , and ones that do bluetooth SAP . Some implement multiple of these profiles and allow you to choose. HSP (head set profile) is the simplest profile: your carkit is basically a speaker-microphone combo, and will play the received audio and send your voice to the telephone. The telephone connects to the cellular network and handles the call. HSP is commonly used in bluetooth earpieces. HFP (hands free profile) is the most common protocol in carkits with a display: your phone still handles the call, and the carkit provides the two-way audio function just like HSP. But the carkit also has basic control over the phone: it can access the received/dialled/missed call lists. It can also instruct the phone to dial a number, to accept or to reject an incoming call. Most carkits also access the phonebook. SAP (SIM access profile, also known as rSAP or SIM) is the most complex of the three: this c...
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