Not to contradict Lou's thoughts about pushing the telco to give you a better line, but... The only non-voice service most tarrifs require is 14.4 fax service. You're likely not going to get them to give a hoot that you can't connect your modem above that data rate. They really have no incentive to get you better dialup service -- even if you can't get residential DSL, they'll be happy to sell you a loop for a fractional T1, SDSL, ISDN, etc.
On top of that, a lot of residential copper is multiplexed, meaning that you share a copper pair with a neighbor. This effectively halves the available bandwidth for your modem. Perfectly within their right to do so. As long as you can make and receive voice calls and get your 14.4 fax through, they can connect you with wet noodles if they want.
I dealt with the phone company for three years when I ran an ISP. Maintaining data circuits in the boonies is a real picnic. As Lou suggests, you might try getting them to check your line, but unless your service is completely out, pretty crappy service passes for acceptable.
Any wireless ISPs in your area? (That's what I ran...) If not, how about satellite? Expensive, but reasonable for most surfing. Failing that, you might be able to get a business class SDSL circuit, or if you are close to your telco switch, a cheap fractional T1. The latter two options will be over $100 a month, but if you're desperate...