Sequencing of ~3,5 kb - (Dec/28/2013 )

although i have done it successfully, using the same primers as for the pcr used to amplify the dna may not work. you should prepare a primer starting a few bases in from the end.

Using PCR primers for sequencing is only a problem if your PCR reaction produces multiple bands or primer dimer products. If you have a good single band, then a PCR primer works well for sequencing. But, as mdfenko says, making a second primer interior to the PCR primer will largely solve this problem, so that you can sequence with relatively impure PCR product.