One of the downfalls of a network that only uses the 1900 MHz GSM band. 850 MHz gives better in-building performance. You may find a handset that improves it a bit, but your best bet is to go with a carrier that offers 850/1900 bands.

there is typically problems associated w/ being inside buildings, getting on a carrier w/ an 850mhz frequency will NOT solve this problem, its an antenna (with the phone)/building conflict, you could get a repeater for your house, but thats a pricey solution (to the tune of around $700), tell them to make the building a super conductor 😁