there are 8 bits in a byte so 49000 might get you 6.1kBPS at best with no overhead
Inside the building, the customer can make sure the modem is on a dedicated line with good wire, no extensions or faxes or answering machines. You can try different ISPs as they may be at different distances and their modems may not play well with yours.
Upgrading the modems firmware and drivers may help
v.92 is a slightly better modem standard, and external modems are traditionally less parasitic on CPU cycles. cable and DSL are faster than dial up, wireless and satelite MAYbe as well
I tried to remain child-like, all I acheived was childish.