If you want to connect the 2 modems to 1 telephone line, it's possible, it's just the same thing when you connect this 1 telephone line to 2 telephones, one in your bedroom and the other in the Hall or whatever.
You will have to get a nice cheap splitter, which will allow you to split the phone cable to 2 and connect 1 to each modem.
The main thing here is that I don't know what exactly are you asking about? Are you asking if you can combine the 2 modems to get higher speed, No this is not possible, because you have just 1 phone line and it has a limited speed over dial up.
If you are asking if you can just connect the 1 line to both modems and use just 1 one of them to connect to your ISP at a given time, then yes, this is possible, but as long as 1 modem is connected, you can't use the other one, or it will simply disconnect the already connected one.
This is useful if you have 2 PCs at 2 different locations inside your house and need to connect to the internet from any PC, if this is what you mean, then Yes, this is possible and very simple.