This may be a blunder question. But just for my curiosity Is it possible to use more tha one modem to connect to internet time,To increase speed . If yes How? If No why?
Your question results in answers more complex than you may imagine.
First off, there are many ways to do this, with different benefits and complexity. I don't know them all, but I am going to cover what I do know.
1) Load-balancing. Load balancing takes two connections, analyzes the connection quality per connection (as in typically per application connection) and chooses the best route between the two routes (two modems). This does not typically result in a doubling of bandwidth, it typically is better for redundancy (uptime) and best-routes. It can result in more available bandwidth for many different connections, say for lots of people, but does not combine bandwidth for single connections.
2) Connection Teaming/Bonding. Teaming/Bonding can be done many ways, but typically it requires identical modems, and identical routing/switching hardware on both your end and the ISP's end. Your ISP has to configure their router/switch to team/bond the connection in the same method you use (there are different protocols), and then so does yours. If this is done properly it should combine the bandwidth. Typically ISPs will charge extra for this service, and it's not going to come cheap. Not all teaming/bonding protocols include redundancy/fail-over built in, but consider that if your ISP goes down, so does your entire connection.
3) Multicasting. I'm not sure if it's possible but I've heard rumor that multicasting can be configured somehow to combine bandwidth. I have not seen a known good configuration just yet.
Load-balancing is the easiest to setup, typically should incur no cost from your ISP, and enables you to get connections from different ISPs.