ChatterBank3 mins ago
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The most common reason for using two SIM cards are if you travel between two countries a lot, and want to use the cheapest provider in each of the countries. Another reason might be to use different phone numbers for private and business use. The only disadvantages (that I can think of) are that dual-SIM phones tend to cost more, and with most such phones you need to manually select which SIM is active at any time (so if you select, say, the business SIM, then your incoming private calls will go to voicemail, and vice versa).